Unit - 2

Structures, Union and File Handling

Q1) Define structure? Explain how to access elements in structures?

A1) Structure

A structure can be considered as a template used for defining a collection of variables under a single name. Structures help programmers to group elements of different data types into a single logical unit (Unlike arrays which permit a programmer to group only elements of same data type).

Why Use Structures

•         Ordinary variables can hold one piece of information

•         arrays can hold a number of pieces of information of the same data type.

For example, suppose you want to store data about a book. You might want to  store its name (a string), its price (a float) and number of pages in it (an int).

If data about say 3 such books is to be stored, then we can follow two approaches:

• Construct individual arrays, one for storing names, another for storing prices and still another for storing number of pages.
• Use a structure variable.

Suppose we want to create a employee database. Then, we can define a structure called employee with three elements id, name and salary. The syntax of this structure is as follows:

Struct employee

{   int id;

Char name[50];

Float salary;

};

Q2) Explain structure variable declaration?

A2) Structure variable

We can declare the variable of structure in two ways

1. Declare the structure inside main function
2. Declare the structure outside the main function.

1. Declare the structure inside main function

Following example show you, how structure variable is declared inside main function

Struct employee

{

Int id;

Char name[50];

Float salary;

};

Int main()

{

Struct employee e1, e2;

Return 0;

}

In this example the variable of structure employee is created inside main function that e1 ,e2.

2. Declare the structure outside main function

Following example show you, how structure variable is declared outside the main function

Struct employee

{

Int id;

Char name[50];

Float salary;

}e1,e2;

Q3) How do you declare structures for multiple variables?

A3) Declaration

Struct student

{

Char name[20];

Int roll;

Float marks;

}

Std1 = {"Poonam" ,67, 78.3};

Std2 = {"Vishal",62, 71.3};

In this example, we have declared two structure variables in above code. After declaration of variable we have initialized two variable.

Std1 = {"Poonam" ,67, 78.3};

Std2 = {"Vishal",62, 71.3};

Q4) How do you access structure elements in the array?

A4) Access structure element in array

Structure is a collection of different data types. An object of structure represents a single record in memory, if we want more than one record of structure type, we have to create an array of structure or object. As we know, an array is a collection of similar type, therefore an array can be of structure type.

Syntax for declaring structure array

Struct struct-name

{

Datatype var1;

Datatype var2;

- - - - - - - - - -

- - - - - - - - - -

Datatype varN;

};

Struct struct-name obj [ size ];

Example for declaring structure array

#include<stdio.h>

Struct Employee

{

Int Id;

Char Name[25];

Int Age;

Long Salary;

};

Void main()

{

Int i;

Struct Employee Emp[ 3 ]; //Statement 1

For(i=0;i<3;i++)

{

Printf("\nEnter details of %d Employee",i+1);

Printf("\n\tEnter Employee Id : ");

Scanf("%d",&Emp[i].Id);

Printf("\n\tEnter Employee Name : ");

Scanf("%s",&Emp[i].Name);

Printf("\n\tEnter Employee Age : ");

Scanf("%d",&Emp[i].Age);

Printf("\n\tEnter Employee Salary : ");

Scanf("%ld",&Emp[i].Salary);

}

Printf("\nDetails of Employees");

For(i=0;i<3;i++)

Printf("\n%d\t%s\t%d\t%ld",Emp[i].Id,Emp[i].Name,Emp[i].Age,Emp[i].Salary);

}

Output:

Enter details of 1 Employee

Enter Employee Id : 101

Enter Employee Name : Suresh

Enter Employee Age : 29

Enter Employee Salary : 45000

Enter details of 2 Employee

Enter Employee Id : 102

Enter Employee Name : Mukesh

Enter Employee Age : 31

Enter Employee Salary : 51000

Enter details of 3 Employee

Enter Employee Id : 103

Enter Employee Name : Ramesh

Enter Employee Age : 28

Enter Employee Salary : 47000

Details of Employees

101 Suresh 29 45000

102 Mukesh 31 51000

103 Ramesh 28 47000

In the above example, we are getting and displaying the data of 3 employee using array of object. Statement 1 is creating an array of Employee Emp to store the records of 3 employees.

Array within Structure

As we know, structure is collection of different data type. Like normal data type, It can

Also store an array as well.

Syntax for array within structure

Struct struct-name

{

Datatype var1; // normal variable

Datatype array [size]; // array variable

- - - - - - - - - -

- - - - - - - - - -

Datatype varN;

};

Struct struct-name obj;

Example for array within structure

Struct Student

{

Int Roll;

Char Name[25];

Int Marks[3]; //Statement 1 : array of marks

Int Total;

Float Avg;

};

Void main()

{

Int i;

Struct Student S;

Printf("\n\nEnter Student Roll : ");

Scanf("%d",&S.Roll);

Printf("\n\nEnter Student Name : ");

Scanf("%s",&S.Name);

S.Total = 0;

For(i=0;i<3;i++)

{

Printf("\n\nEnter Marks %d : ",i+1);

Scanf("%d",&S.Marks[i]);

S.Total = S.Total + S.Marks[i];

}

S.Avg = S.Total / 3;

Printf("\nRoll : %d",S.Roll);

Printf("\nName : %s",S.Name);

Printf("\nTotal : %d",S.Total);

Printf("\nAverage : %f",S.Avg);

}

Output:

Enter Student Roll : 10

Enter Student Name : Kumar

Enter Marks 1 : 78

Enter Marks 2 : 89

Enter Marks 3 : 56

Roll : 10

Name : Kumar

Total : 223

Average: 74.00000

In the above example, we have created an array Marks[ ] inside structure representing 3 marks of a single student. Marks[ ] is now a member of structure student and to access Marks[ ] we have used dot operator(.) along with object S.

Q5) Write a program to obtain the details of the 3 employees?

A5) Program

#include <iostream>

Using namespace std;

Struct employee {

String ename;

Int age, phn_no;

Int salary;

};

// Function to display details of all employees

Void display(struct employee emp[], int n)

{

Cout<< "Name\tAge\tPhone Number\tSalary\n";

For (int i = 0; i< n; i++) {

Cout<< emp[i].ename<< "\t" << emp[i].age << "\t"

<< emp[i].phn_no<< "\t" << emp[i].salary << "\n";

}

}

// Driver code

Int main()

{

Int n = 3;

// Array of structure objects

Struct employee emp[n];

// Details of employee 1

Emp[0].ename = "Chirag";

Emp[0].age = 24;

Emp[0].phn_no = 1234567788;

Emp[0].salary = 20000;

// Details of employee 2

Emp[1].ename = "Arnav";

Emp[1].age = 31;

Emp[1].phn_no = 1234567891;

Emp[1].salary = 56000;

// Details of employee 3

Emp[2].ename = "Shivam";

Emp[2].age = 45;

Emp[2].phn_no = 1100661111;

Emp[2].salary = 30500;

Display(emp, n);

Return 0;

}

Output:

Name     Age    Phone Number   Salary

Chirag   24     1234567788      20000

Arnav    31     1234567891      56000

Shivam   45     8881101111      30500

Q6) Define union?

A6) Union

Unions are quite similar to the structures in C. Union is also a derived type as structure. Union can be defined in same manner as structures just the keyword used in defining union in union where keyword used in defining structure was struct.

Union car

{

Char name[50];

Int price;

};

Union variables can be created in similar manner as structure variable.

Union car

{

Char name[50];

Int price;

}c1, c2, *c3;

OR;

Union car

{

Char name[50];

Int price;

};

-------Inside Function-----------

Union car c1, c2, *c3;

In both cases, union variables c1, c2 and union pointer variable c3 of type union car is created.

Q7) How do you access the members of the union?

A7) Access member of union

●       Array elements are accessed using the Subscript variable , Similarly Union members are accessed using dot [.] operator.

●       (.) is called as “union member Operator”.

●       Use this Operator in between “Union variable”&“member name”

Union employee

{

Int id;

Char name[50];

Float salary;

} ;

Void main()

{

Union employee e1= { 1, “ABC”, 50000 };

Printf(“%d”, e. Id);

Printf(“%s”, e. Name);

}

O/P-  garbage value, ABC

Q8) Compare structure and union?

A8) Structure Vs Union

Q9) Write a program to store information of students and display it?

A9) Program

#include <stdio.h>

#include <string.h>

Union Student

{

Int age;

Char Name[50];

Char Department[20];

};

Int main()

{

Union student stud1;

Union Employee stud2;

Stud1.age = 28;

Strcpy(stud1.Name, "Chris");

Strcpy(stud1.Department, "Science");

Printf("\nDetails of the First Student \n");

Printf("  Student Age = %d \n", emp1.age);

Printf("  Student Name = %s \n", emp1.Name);

Printf("  Student Department = %s \n", emp1.Department);

Printf("Details of the Second Student \n" );

Stud2.age = 30;

Printf("  Student Age = %d \n", stud2.age );

Strcpy(stud2.Name, "David");

Printf("  Student Name = %s \n", stud2.Name );

Strcpy(stud2.Department, "Technology" );

Printf("  Student Department = %s \n ", stud2.Department );

Return 0;

}

OUTPUT:

Details of the first student

Student Age = 28

Student Name = Chris

Student Department = Science

Details of the Second Student

Student Age =30

Student Name = David

Student Department= Technology

Q10) Write the advantages and disadvantages of structure?

A10) Advantages of structure

●       Structures gather more than one piece of data about the same subject together in the same place.

●       It is helpful when you want to gather the data of similar data types and parameters like first name, last name, etc.

●       It is very easy to maintain as we can represent the whole record by using a single name.

●       In structure, we can pass a complete set of records to any function using a single parameter.

●       You can use an array of structure to store more records with similar types.

Disadvantages of structure

●       If the complexity of an IT project goes beyond the limit, it becomes hard to manage.

●       Change of one data structure in a code necessitates changes at many other places. Therefore, the changes become hard to track.

●       Structure is slower because it requires storage space for all the data.

●       You can retrieve any member at a time in structure whereas you can access one member at a time in the union.

●       Structure occupies space for each and every member written in inner parameters while union occupies space for a member having the highest size written in inner parameters.

●       Structure supports a flexible array. Union does not support a flexible array.

Q11) Write an example for calloc ()?

A11) Program

Example of calloc()

#include<stdio.h>

#include<stdlib.h>

Int main()

{

Int n,i,*ptr,sum=0;

Printf("Enter number of elements: ");

Scanf("%d",&n);

Ptr=(int*)calloc(n,sizeof(int));  //memory allocated using calloc

If(ptr==NULL)

{

Printf("Sorry! unable to allocate memory");

Exit(0);

}

Printf("Enter elements of array: ");

For(i=0;i<n;++i)

{

Scanf("%d",ptr+i);

Sum+=*(ptr+i);

}

Printf("Sum=%d",sum);

Free(ptr);

Return 0;

}

Output

Enter elements of array: 3

Enter elements of array: 10

10

10

Sum=30

Q12) Explain nested structure?

A12) The feature of nesting one structure within another structure in C allows us to design complicated data types. For example, we could need to keep an entity employee's address in a structure. Street number, city, state, and pin code are all possible subparts of the attribute address. As a result, we must store the employee's address in a different structure and nest the structure address into the structure employee to store the employee's address.

In the following methods, the structure can be nested.

●      By separate structure

●      By Embedded structure

1) Separate structure

We've created two structures here, but the dependent structure should be utilised as a member inside the primary structure. Consider the following illustration.

Struct Date 

{ 

   int dd; 

   int mm; 

   int yyyy;  

}; 

Struct Employee 

{    

   int id; 

   char name[20]; 

   struct Date doj; 

}emp1; 

Doj (date of joining) is a Date variable, as you can see. In this case, doj is a member of the Employee structure. We may utilise the Date structure in a variety of structures this way.

2) Embedded structure

We can declare the structure inside the structure using the embedded structure. As a result, it uses fewer lines of code, but it cannot be applied to numerous data structures. Consider the following illustration.

Struct Employee 

{    

   int id; 

   char name[20]; 

   struct Date 

    { 

      int dd; 

      int mm; 

      int yyyy;  

    }doj; 

}emp1; 

Accessing Nested Structure

We can access the member of the nested structure by

Outer_Structure.Nested_Structure.member as given below:

e1.doj.dd 

e1.doj.mm

e1.doj.yyyy 

Example of Nested Structure

#include <stdio.h> 

#include <string.h> 

Struct Employee 

{    

   int id; 

   char name[20]; 

   struct Date 

    { 

      int dd; 

      int mm; 

      int yyyy;  

    }doj; 

}e1; 

Int main( ) 

{ 

   //storing employee information 

   e1.id=101; 

   strcpy(e1.name, "Sonoo Jaiswal");//copying string into char array 

   e1.doj.dd=10; 

   e1.doj.mm=11; 

   e1.doj.yyyy=2014; 

   //printing first employee information 

   printf( "employee id : %d\n", e1.id); 

   printf( "employee name : %s\n", e1.name); 

   printf( "employee date of joining (dd/mm/yyyy) : %d/%d/%d\n", e1.doj.dd,e1.doj.mm,e1.doj.yyyy); 

   return 0; 

}

Output:

Employee id : 101

Employee name : Sonoo Jaiswal

Employee date of joining (dd/mm/yyyy) : 10/11/2014

Q13) Write a program for nested strcuture?

A13) Consider the programme below.

#include<stdio.h> 

Struct address  

{ 

    char city[20]; 

    int pin; 

    char phone[14]; 

}; 

Struct employee 

{ 

    char name[20]; 

    struct address add; 

}; 

Void main () 

{ 

    struct employee emp; 

    printf("Enter employee information?\n"); 

    scanf("%s %s %d %s",emp.name,emp.add.city, &emp.add.pin, emp.add.phone); 

    printf("Printing the employee information....\n"); 

    printf("name: %s\nCity: %s\nPincode: %d\nPhone: %s",emp.name,emp.add.city,emp.add.pin,emp.add.phone); 

} 

Output

Enter employee information?

Arun           

Delhi          

110001      

1234567890   

Printing the employee information....  

Name: Arun     

City: Delhi 

Pincode: 110001

Phone: 1234567890

Q14) Describe an Array of structure with an example?

A14) In C, an array of structures is a collection of many structure variables, each of which contains information on a different entity. In C, an array of structures is used to store data about many entities of various data kinds. The collection of structures is another name for the array of structures.

Fig 1: Array of structure

Let's look at an array of structures that stores and outputs information for five students.

#include<stdio.h> 

#include <string.h>   

Struct student{   

Int rollno;   

Char name[10];   

};   

Int main(){   

Int i;   

Struct student st[5];   

Printf("Enter Records of 5 students");   

For(i=0;i<5;i++){   

Printf("\nEnter Rollno:");   

Scanf("%d",&st[i].rollno);   

Printf("\nEnter Name:");   

Scanf("%s",&st[i].name);   

}   

Printf("\nStudent Information List:");   

For(i=0;i<5;i++){   

Printf("\nRollno:%d, Name:%s",st[i].rollno,st[i].name);   

}   

   return 0;   

}  

Output:

Enter Records of 5 students

Enter Rollno:10

Enter Name:Sonu

Enter Rollno:20

Enter Name:Ratana

Enter Rollno:30

Enter Name:Vomika

Enter Rollno:40

Enter Name:James

Enter Rollno:50

Enter Name:Sadaf

Student Information List:

Rollno:10, Name:Sonu

Rollno:20, Name:Ratanaa

Rollno:30, Name:Vomika

Rollno:40, Name:James

Rollno:50, Name:Sadaf

Q15) Write a Program to access the structure member using the structure pointer and arrow (->) operator?

A15) Consider a C programme that uses the pointer and the arrow (->) operator to access structure members.

#include <stdio.h>

// create Employee structure  

Struct Employee 

{ 

    // define the member of the structure 

    char name[30]; 

    int id; 

    int age; 

    char gender[30]; 

    char city[40]; 

}; 

// define the variables of the Structure with pointers 

Struct Employee emp1, emp2, *ptr1, *ptr2; 

Int main() 

{ 

    // store the address of the emp1 and emp2 structure variable 

    ptr1 = &emp1; 

    ptr2 = &emp2; 

    printf (" Enter the name of the Employee (emp1): "); 

    scanf (" %s", &ptr1->name); 

    printf (" Enter the id of the Employee (emp1): "); 

    scanf (" %d", &ptr1->id); 

    printf (" Enter the age of the Employee (emp1): "); 

    scanf (" %d", &ptr1->age); 

    printf (" Enter the gender of the Employee (emp1): "); 

    scanf (" %s", &ptr1->gender); 

    printf (" Enter the city of the Employee (emp1): "); 

    scanf (" %s", &ptr1->city); 

    printf (" \n Second Employee: \n"); 

            printf (" Enter the name of the Employee (emp2): "); 

    scanf (" %s", &ptr2->name); 

    printf (" Enter the id of the Employee (emp2): "); 

    scanf (" %d", &ptr2->id); 

    printf (" Enter the age of the Employee (emp2): "); 

    scanf (" %d", &ptr2->age); 

    printf (" Enter the gender of the Employee (emp2): "); 

    scanf (" %s", &ptr2->gender); 

    printf (" Enter the city of the Employee (emp2): "); 

    scanf (" %s", &ptr2->city); 

    printf ("\n Display the Details of the Employee using Structure Pointer"); 

    printf ("\n Details of the Employee (emp1) \n"); 

    printf(" Name: %s\n", ptr1->name); 

    printf(" Id: %d\n", ptr1->id); 

    printf(" Age: %d\n", ptr1->age); 

    printf(" Gender: %s\n", ptr1->gender); 

    printf(" City: %s\n", ptr1->city); 

    printf ("\n Details of the Employee (emp2) \n"); 

    printf(" Name: %s\n", ptr2->name); 

    printf(" Id: %d\n", ptr2->id); 

    printf(" Age: %d\n", ptr2->age); 

    printf(" Gender: %s\n", ptr2->gender); 

    printf(" City: %s\n", ptr2->city); 

    return 0; 

}  

Output:

Enter the name of the Employee (emp1): John

Enter the id of the Employee (emp1): 1099

Enter the age of the Employee (emp1): 28

Enter the gender of the Employee (emp1): Male

Enter the city of the Employee (emp1): California

Second Employee: 

Enter the name of the Employee (emp2): Maria

Enter the id of the Employee (emp2): 1109

Enter the age of the Employee (emp2): 23

Enter the gender of the Employee (emp2): Female

Enter the city of the Employee (emp2): Los Angeles

Display the Details of the Employee using Structure Pointer

Details of the Employee (emp1)

Name: John

Id: 1099

Age: 28

Gender: Male

City: California

Details of the Employee (emp2) Name: Maria

Id: 1109

Age: 23

Gender: Female

City: Los Angeles

Q16) Write a Program to access the structure member using structure pointer and the dot operator?

A16) Consider the following example of creating a Subject structure and accessing its components with a structure pointer that points to the Subject variable's address in C.

#include <stdio.h> 

// create a structure Subject using the struct keyword 

Struct Subject 

{ 

    // declare the member of the Course structure 

    char sub_name[30]; 

    int sub_id; 

    char sub_duration[50]; 

    char sub_type[50]; 

}; 

Int main() 

{ 

    struct Subject sub; // declare the Subject variable 

    struct Subject *ptr; // create a pointer variable (*ptr)  

    ptr = ⊂ /* ptr variable pointing to the address of the structure variable sub */ 

    strcpy (sub.sub_name, " Computer Science"); 

    sub.sub_id = 1201; 

    strcpy (sub.sub_duration, "6 Months"); 

    strcpy (sub.sub_type, " Multiple Choice Question"); 

    // print the details of the Subject; 

    printf (" Subject Name: %s\t ", (*ptr).sub_name); 

            printf (" \n Subject Id: %d\t ", (*ptr).sub_id); 

        printf (" \n Duration of the Subject: %s\t ", (*ptr).sub_duration); 

           printf (" \n Type of the Subject: %s\t ", (*ptr).sub_type); 

    return 0; 

} 

Output:

Subject Name: Computer Science

Subject Id: 1201

Duration of the Subject: 6 Months

Type of the Subject: Multiple Choice Question

Q17) What is sizeof ()?

A17) In C, the sizeof() operator is frequently used. It determines the number of char-sized storage units used to store the expression or data type. The sizeof() operator has only one operand, which can either be an expression or a data typecast with the cast encapsulated in parenthesis. The data type can be pointer data types or complex data types like unions and structs, in addition to primitive data types like integer and floating data types.

Need of sizeof() operator

The storage size of basic data types is mostly known by programmes. The data type's storage size is constant, but it differs when implemented on different platforms. For example, we dynamically allocate the array space by using sizeof() operator:

Int *ptr=malloc(10*sizeof(int)); 

The sizeof() operation is applied to the cast of type int in the preceding example. The malloc() method is used to allocate memory and returns a reference to the memory that has been allocated. The memory space is calculated by multiplying the amount of bytes occupied by the int data type by ten.

Depending on the kind of operand, the sizeof() operator operates differently.

●      Operand is a data type

●      Operand is an expression

Q18) Define typedef?

A18) typedef

The typedef keyword is used in C programming to give meaningful names to variables that already exist in the programme. It works similarly to how we construct aliases for commands. In a nutshell, this keyword is used to change the name of a variable that already exists.

Syntax of typedef

Typedef <existing_name> <alias_name> 

'existing name' is the name of an already existing variable in the aforementioned syntax, while 'alias name' is another name for the same variable.

If we wish to create a variable of type unsigned int, for example, it will be a time-consuming operation if we want to declare several variables of this kind. We utilise the typedef keyword to solve the problem.

Typedef unsigned int unit; 

We used the typedef keyword to declare the unsigned int unit variable in the above statements.

By writing the following statement, we can now create variables of type unsigned int:

Unit a, b;  

Rather than writing:

Unsigned int a, b; 

So far, we've seen how the typedef keyword provides a convenient shortcut by offering an alternate name for a variable that already exists. This keyword comes in handy when working with lengthy data types, particularly structure declarations.

Example

#include <stdio.h> 

Int main() 

{ 

Typedef unsigned int unit; 

Unit i,j; 

i=10; 

j=20; 

Printf("Value of i is :%d",i); 

Printf("\nValue of j is :%d",j); 

Return 0; 

}

Output

Value of i is :10

Value of j is :20

Q19) Write notes on - fseek(), ftell() and rewind()?

A19) fseek()

To set the file pointer to a certain offset, use the fseek() function. It's used to save data to a file at a certain location.

Syntax:

Int fseek(FILE *stream, long int offset, int whence) 

Whence, the fseek() function uses three constants: SEEK SET, SEEK CUR, and SEEK END.

Example

#include <stdio.h> 

Void main(){ 

   FILE *fp; 

   fp = fopen("myfile.txt","w+"); 

   fputs("This is javatpoint", fp); 

   fseek( fp, 7, SEEK_SET ); 

   fputs("sonoo jaiswal", fp); 

   fclose(fp); 

} 

Output

This is sonam jaiswal

Ftell()

The ftell() function returns the supplied stream's current file position. After shifting the file pointer to the end of the file, we can use the ftell() function to retrieve the total size of the file. The SEEK END constant can be used to relocate the file pointer to the end of the file.

Syntax:

Long int ftell(FILE *stream) 

Example

#include <stdio.h> 

#include <conio.h> 

Void main (){ 

   FILE *fp; 

   int length; 

   clrscr(); 

   fp = fopen("file.txt", "r"); 

   fseek(fp, 0, SEEK_END); 

   length = ftell(fp); 

   fclose(fp); 

   printf("Size of file: %d bytes", length); 

   getch(); 

} 

Output:

Size of file: 21 bytes

Rewind()

The file pointer is set to the beginning of the stream using the rewind() function. It's useful if you'll be using stream frequently.

Syntax:

Void rewind(FILE *stream) 

Example

#include<stdio.h> 

#include<conio.h> 

Void main(){ 

FILE *fp; 

Char c; 

Clrscr(); 

Fp=fopen("file.txt","r"); 

While((c=fgetc(fp))!=EOF){ 

Printf("%c",c); 

} 

Rewind(fp);//moves the file pointer at beginning of the file 

While((c=fgetc(fp))!=EOF){ 

Printf("%c",c); 

} 

Fclose(fp);   

Getch();   

}   

Output:

This is a simple textthis is a simple text

The rewind() function, as you can see, moves the file pointer to the beginning of the file, which is why "this is simple text" is printed twice. If the rewind() function is not used, "this is simple text" will only be printed once.

Q20) What are the formatted input?

A20) scanf()

We utilize the scanf() function to get formatted or standard inputs so that the printf() function can give the programme a variety of conversion possibilities.

Syntax for scanf()

Scanf (format_specifier, &data_a, &data_b,……); // Here, & refers to the address operator

The scanf() function's goal is to read the characters from the standard input, convert them according to the format string, and then store the accessible inputs in the memory slots represented by the other arguments.

Example of scanf()

Scanf(“%d %c”, &info_a,&info_b);

The '&' character does not preface the data name when considering string data names in a programme.

Sscanf()

Int sscanf(const char *str, const char *format,...) is a C function that reads formatted input from a string.

Declaration

The sscanf() function is declared as follows.

Int sscanf(const char *str, const char *format, ...)

Parameters

●      str - This is the C string that the function uses as its data source.

●      format - is a C string that contains one or more of the items listed below: Format specifiers, whitespace characters, and non-whitespace characters

This prototype is followed by a format specifier: [=%[*] [width] [modifiers]type=]

Fscanf()

To read a collection of characters from a file, use the fscanf() method. It reads a single word from the file and returns EOF when the file reaches the end.

Syntax:

Int fscanf(FILE *stream, const char *format [, argument, ...]) 

Example:

#include <stdio.h> 

Main(){ 

   FILE *fp; 

   char buff[255];//creating char array to store data of file 

   fp = fopen("file.txt", "r"); 

   while(fscanf(fp, "%s", buff)!=EOF){ 

   printf("%s ", buff ); 

   } 

   fclose(fp); 

} 

Output:

Hello file by fprintf...

Fread()

The fread() function is the fwrite() function's counterpart. To read binary data, the fread() function is widely used. It takes the same parameters as the fwrite() function. The fread() method has the following syntax:

Syntax:

Size_t fread(void *ptr, size_t size, size_t n, FILE *fp);

After reading from the file, the ptr is the starting address of the RAM block where data will be stored. The function reads n items from the file, each of which takes up the amount of bytes indicated in the second argument. It reads n items from the file and returns n if it succeeds. It returns a number smaller than n in the event of an error or the end of the file.

Example

Reading a structure array

Struct student

{

    char name[10];

    int roll;

    float marks;

};

Struct student arr_student[100];

Fread(&arr_student, sizeof(struct student), 10, fp);

This reads the first 10 struct student elements from the file and places them in the arr_studen variable.

Unit - 2

Structures, Union and File Handling

Q1) Define structure? Explain how to access elements in structures?

A1) Structure

A structure can be considered as a template used for defining a collection of variables under a single name. Structures help programmers to group elements of different data types into a single logical unit (Unlike arrays which permit a programmer to group only elements of same data type).

Why Use Structures

•         Ordinary variables can hold one piece of information

•         arrays can hold a number of pieces of information of the same data type.

For example, suppose you want to store data about a book. You might want to  store its name (a string), its price (a float) and number of pages in it (an int).

If data about say 3 such books is to be stored, then we can follow two approaches:

• Construct individual arrays, one for storing names, another for storing prices and still another for storing number of pages.
• Use a structure variable.

Suppose we want to create a employee database. Then, we can define a structure called employee with three elements id, name and salary. The syntax of this structure is as follows:

Struct employee

{   int id;

Char name[50];

Float salary;

};

Q2) Explain structure variable declaration?

A2) Structure variable

We can declare the variable of structure in two ways

1. Declare the structure inside main function
2. Declare the structure outside the main function.

1. Declare the structure inside main function

Following example show you, how structure variable is declared inside main function

Struct employee

{

Int id;

Char name[50];

Float salary;

};

Int main()

{

Struct employee e1, e2;

Return 0;

}

In this example the variable of structure employee is created inside main function that e1 ,e2.

2. Declare the structure outside main function

Following example show you, how structure variable is declared outside the main function

Struct employee

{

Int id;

Char name[50];

Float salary;

}e1,e2;

Q3) How do you declare structures for multiple variables?

A3) Declaration

Struct student

{

Char name[20];

Int roll;

Float marks;

}

Std1 = {"Poonam" ,67, 78.3};

Std2 = {"Vishal",62, 71.3};

In this example, we have declared two structure variables in above code. After declaration of variable we have initialized two variable.

Std1 = {"Poonam" ,67, 78.3};

Std2 = {"Vishal",62, 71.3};

Q4) How do you access structure elements in the array?

A4) Access structure element in array

Structure is a collection of different data types. An object of structure represents a single record in memory, if we want more than one record of structure type, we have to create an array of structure or object. As we know, an array is a collection of similar type, therefore an array can be of structure type.

Syntax for declaring structure array

Struct struct-name

{

Datatype var1;

Datatype var2;

- - - - - - - - - -

- - - - - - - - - -

Datatype varN;

};

Struct struct-name obj [ size ];

Example for declaring structure array

#include<stdio.h>

Struct Employee

{

Int Id;

Char Name[25];

Int Age;

Long Salary;

};

Void main()

{

Int i;

Struct Employee Emp[ 3 ]; //Statement 1

For(i=0;i<3;i++)

{

Printf("\nEnter details of %d Employee",i+1);

Printf("\n\tEnter Employee Id : ");

Scanf("%d",&Emp[i].Id);

Printf("\n\tEnter Employee Name : ");

Scanf("%s",&Emp[i].Name);

Printf("\n\tEnter Employee Age : ");

Scanf("%d",&Emp[i].Age);

Printf("\n\tEnter Employee Salary : ");

Scanf("%ld",&Emp[i].Salary);

}

Printf("\nDetails of Employees");

For(i=0;i<3;i++)

Printf("\n%d\t%s\t%d\t%ld",Emp[i].Id,Emp[i].Name,Emp[i].Age,Emp[i].Salary);

}

Output:

Enter details of 1 Employee

Enter Employee Id : 101

Enter Employee Name : Suresh

Enter Employee Age : 29

Enter Employee Salary : 45000

Enter details of 2 Employee

Enter Employee Id : 102

Enter Employee Name : Mukesh

Enter Employee Age : 31

Enter Employee Salary : 51000

Enter details of 3 Employee

Enter Employee Id : 103

Enter Employee Name : Ramesh

Enter Employee Age : 28

Enter Employee Salary : 47000

Details of Employees

101 Suresh 29 45000

102 Mukesh 31 51000

103 Ramesh 28 47000

In the above example, we are getting and displaying the data of 3 employee using array of object. Statement 1 is creating an array of Employee Emp to store the records of 3 employees.

Array within Structure

As we know, structure is collection of different data type. Like normal data type, It can

Also store an array as well.

Syntax for array within structure

Struct struct-name

{

Datatype var1; // normal variable

Datatype array [size]; // array variable

- - - - - - - - - -

- - - - - - - - - -

Datatype varN;

};

Struct struct-name obj;

Example for array within structure

Struct Student

{

Int Roll;

Char Name[25];

Int Marks[3]; //Statement 1 : array of marks

Int Total;

Float Avg;

};

Void main()

{

Int i;

Struct Student S;

Printf("\n\nEnter Student Roll : ");

Scanf("%d",&S.Roll);

Printf("\n\nEnter Student Name : ");

Scanf("%s",&S.Name);

S.Total = 0;

For(i=0;i<3;i++)

{

Printf("\n\nEnter Marks %d : ",i+1);

Scanf("%d",&S.Marks[i]);

S.Total = S.Total + S.Marks[i];

}

S.Avg = S.Total / 3;

Printf("\nRoll : %d",S.Roll);

Printf("\nName : %s",S.Name);

Printf("\nTotal : %d",S.Total);

Printf("\nAverage : %f",S.Avg);

}

Output:

Enter Student Roll : 10

Enter Student Name : Kumar

Enter Marks 1 : 78

Enter Marks 2 : 89

Enter Marks 3 : 56

Roll : 10

Name : Kumar

Total : 223

Average: 74.00000

In the above example, we have created an array Marks[ ] inside structure representing 3 marks of a single student. Marks[ ] is now a member of structure student and to access Marks[ ] we have used dot operator(.) along with object S.

Q5) Write a program to obtain the details of the 3 employees?

A5) Program

#include <iostream>

Using namespace std;

Struct employee {

String ename;

Int age, phn_no;

Int salary;

};

// Function to display details of all employees

Void display(struct employee emp[], int n)

{

Cout<< "Name\tAge\tPhone Number\tSalary\n";

For (int i = 0; i< n; i++) {

Cout<< emp[i].ename<< "\t" << emp[i].age << "\t"

<< emp[i].phn_no<< "\t" << emp[i].salary << "\n";

}

}

// Driver code

Int main()

{

Int n = 3;

// Array of structure objects

Struct employee emp[n];

// Details of employee 1

Emp[0].ename = "Chirag";

Emp[0].age = 24;

Emp[0].phn_no = 1234567788;

Emp[0].salary = 20000;

// Details of employee 2

Emp[1].ename = "Arnav";

Emp[1].age = 31;

Emp[1].phn_no = 1234567891;

Emp[1].salary = 56000;

// Details of employee 3

Emp[2].ename = "Shivam";

Emp[2].age = 45;

Emp[2].phn_no = 1100661111;

Emp[2].salary = 30500;

Display(emp, n);

Return 0;

}

Output:

Name     Age    Phone Number   Salary

Chirag   24     1234567788      20000

Arnav    31     1234567891      56000

Shivam   45     8881101111      30500

Q6) Define union?

A6) Union

Unions are quite similar to the structures in C. Union is also a derived type as structure. Union can be defined in same manner as structures just the keyword used in defining union in union where keyword used in defining structure was struct.

Union car

{

Char name[50];

Int price;

};

Union variables can be created in similar manner as structure variable.

Union car

{

Char name[50];

Int price;

}c1, c2, *c3;

OR;

Union car

{

Char name[50];

Int price;

};

-------Inside Function-----------

Union car c1, c2, *c3;

In both cases, union variables c1, c2 and union pointer variable c3 of type union car is created.

Q7) How do you access the members of the union?

A7) Access member of union

●       Array elements are accessed using the Subscript variable , Similarly Union members are accessed using dot [.] operator.

●       (.) is called as “union member Operator”.

●       Use this Operator in between “Union variable”&“member name”

Union employee

{

Int id;

Char name[50];

Float salary;

} ;

Void main()

{

Union employee e1= { 1, “ABC”, 50000 };

Printf(“%d”, e. Id);

Printf(“%s”, e. Name);

}

O/P-  garbage value, ABC

Q8) Compare structure and union?

A8) Structure Vs Union

Q9) Write a program to store information of students and display it?

A9) Program

#include <stdio.h>

#include <string.h>

Union Student

{

Int age;

Char Name[50];

Char Department[20];

};

Int main()

{

Union student stud1;

Union Employee stud2;

Stud1.age = 28;

Strcpy(stud1.Name, "Chris");

Strcpy(stud1.Department, "Science");

Printf("\nDetails of the First Student \n");

Printf("  Student Age = %d \n", emp1.age);

Printf("  Student Name = %s \n", emp1.Name);

Printf("  Student Department = %s \n", emp1.Department);

Printf("Details of the Second Student \n" );

Stud2.age = 30;

Printf("  Student Age = %d \n", stud2.age );

Strcpy(stud2.Name, "David");

Printf("  Student Name = %s \n", stud2.Name );

Strcpy(stud2.Department, "Technology" );

Printf("  Student Department = %s \n ", stud2.Department );

Return 0;

}

OUTPUT:

Details of the first student

Student Age = 28

Student Name = Chris

Student Department = Science

Details of the Second Student

Student Age =30

Student Name = David

Student Department= Technology

Q10) Write the advantages and disadvantages of structure?

A10) Advantages of structure

●       Structures gather more than one piece of data about the same subject together in the same place.

●       It is helpful when you want to gather the data of similar data types and parameters like first name, last name, etc.

●       It is very easy to maintain as we can represent the whole record by using a single name.

●       In structure, we can pass a complete set of records to any function using a single parameter.

●       You can use an array of structure to store more records with similar types.

Disadvantages of structure

●       If the complexity of an IT project goes beyond the limit, it becomes hard to manage.

●       Change of one data structure in a code necessitates changes at many other places. Therefore, the changes become hard to track.

●       Structure is slower because it requires storage space for all the data.

●       You can retrieve any member at a time in structure whereas you can access one member at a time in the union.

●       Structure occupies space for each and every member written in inner parameters while union occupies space for a member having the highest size written in inner parameters.

●       Structure supports a flexible array. Union does not support a flexible array.

Q11) Write an example for calloc ()?

A11) Program

Example of calloc()

#include<stdio.h>

#include<stdlib.h>

Int main()

{

Int n,i,*ptr,sum=0;

Printf("Enter number of elements: ");

Scanf("%d",&n);

Ptr=(int*)calloc(n,sizeof(int));  //memory allocated using calloc

If(ptr==NULL)

{

Printf("Sorry! unable to allocate memory");

Exit(0);

}

Printf("Enter elements of array: ");

For(i=0;i<n;++i)

{

Scanf("%d",ptr+i);

Sum+=*(ptr+i);

}

Printf("Sum=%d",sum);

Free(ptr);

Return 0;

}

Output

Enter elements of array: 3

Enter elements of array: 10

10

10

Sum=30

Q12) Explain nested structure?

A12) The feature of nesting one structure within another structure in C allows us to design complicated data types. For example, we could need to keep an entity employee's address in a structure. Street number, city, state, and pin code are all possible subparts of the attribute address. As a result, we must store the employee's address in a different structure and nest the structure address into the structure employee to store the employee's address.

In the following methods, the structure can be nested.

●      By separate structure

●      By Embedded structure

1) Separate structure

We've created two structures here, but the dependent structure should be utilised as a member inside the primary structure. Consider the following illustration.

Struct Date 

{ 

   int dd; 

   int mm; 

   int yyyy;  

}; 

Struct Employee 

{    

   int id; 

   char name[20]; 

   struct Date doj; 

}emp1; 

Doj (date of joining) is a Date variable, as you can see. In this case, doj is a member of the Employee structure. We may utilise the Date structure in a variety of structures this way.

2) Embedded structure

We can declare the structure inside the structure using the embedded structure. As a result, it uses fewer lines of code, but it cannot be applied to numerous data structures. Consider the following illustration.

Struct Employee 

{    

   int id; 

   char name[20]; 

   struct Date 

    { 

      int dd; 

      int mm; 

      int yyyy;  

    }doj; 

}emp1; 

Accessing Nested Structure

We can access the member of the nested structure by

Outer_Structure.Nested_Structure.member as given below:

e1.doj.dd 

e1.doj.mm

e1.doj.yyyy 

Example of Nested Structure

#include <stdio.h> 

#include <string.h> 

Struct Employee 

{    

   int id; 

   char name[20]; 

   struct Date 

    { 

      int dd; 

      int mm; 

      int yyyy;  

    }doj; 

}e1; 

Int main( ) 

{ 

   //storing employee information 

   e1.id=101; 

   strcpy(e1.name, "Sonoo Jaiswal");//copying string into char array 

   e1.doj.dd=10; 

   e1.doj.mm=11; 

   e1.doj.yyyy=2014; 

   //printing first employee information 

   printf( "employee id : %d\n", e1.id); 

   printf( "employee name : %s\n", e1.name); 

   printf( "employee date of joining (dd/mm/yyyy) : %d/%d/%d\n", e1.doj.dd,e1.doj.mm,e1.doj.yyyy); 

   return 0; 

}

Output:

Employee id : 101

Employee name : Sonoo Jaiswal

Employee date of joining (dd/mm/yyyy) : 10/11/2014

Q13) Write a program for nested strcuture?

A13) Consider the programme below.

#include<stdio.h> 

Struct address  

{ 

    char city[20]; 

    int pin; 

    char phone[14]; 

}; 

Struct employee 

{ 

    char name[20]; 

    struct address add; 

}; 

Void main () 

{ 

    struct employee emp; 

    printf("Enter employee information?\n"); 

    scanf("%s %s %d %s",emp.name,emp.add.city, &emp.add.pin, emp.add.phone); 

    printf("Printing the employee information....\n"); 

    printf("name: %s\nCity: %s\nPincode: %d\nPhone: %s",emp.name,emp.add.city,emp.add.pin,emp.add.phone); 

} 

Output

Enter employee information?

Arun           

Delhi          

110001      

1234567890   

Printing the employee information....  

Name: Arun     

City: Delhi 

Pincode: 110001

Phone: 1234567890

Q14) Describe an Array of structure with an example?

A14) In C, an array of structures is a collection of many structure variables, each of which contains information on a different entity. In C, an array of structures is used to store data about many entities of various data kinds. The collection of structures is another name for the array of structures.

Fig 1: Array of structure

Let's look at an array of structures that stores and outputs information for five students.

#include<stdio.h> 

#include <string.h>   

Struct student{   

Int rollno;   

Char name[10];   

};   

Int main(){   

Int i;   

Struct student st[5];   

Printf("Enter Records of 5 students");   

For(i=0;i<5;i++){   

Printf("\nEnter Rollno:");   

Scanf("%d",&st[i].rollno);   

Printf("\nEnter Name:");   

Scanf("%s",&st[i].name);   

}   

Printf("\nStudent Information List:");   

For(i=0;i<5;i++){   

Printf("\nRollno:%d, Name:%s",st[i].rollno,st[i].name);   

}   

   return 0;   

}  

Output:

Enter Records of 5 students

Enter Rollno:10

Enter Name:Sonu

Enter Rollno:20

Enter Name:Ratana

Enter Rollno:30

Enter Name:Vomika

Enter Rollno:40

Enter Name:James

Enter Rollno:50

Enter Name:Sadaf

Student Information List:

Rollno:10, Name:Sonu

Rollno:20, Name:Ratanaa

Rollno:30, Name:Vomika

Rollno:40, Name:James

Rollno:50, Name:Sadaf

Q15) Write a Program to access the structure member using the structure pointer and arrow (->) operator?

A15) Consider a C programme that uses the pointer and the arrow (->) operator to access structure members.

#include <stdio.h>

// create Employee structure  

Struct Employee 

{ 

    // define the member of the structure 

    char name[30]; 

    int id; 

    int age; 

    char gender[30]; 

    char city[40]; 

}; 

// define the variables of the Structure with pointers 

Struct Employee emp1, emp2, *ptr1, *ptr2; 

Int main() 

{ 

    // store the address of the emp1 and emp2 structure variable 

    ptr1 = &emp1; 

    ptr2 = &emp2; 

    printf (" Enter the name of the Employee (emp1): "); 

    scanf (" %s", &ptr1->name); 

    printf (" Enter the id of the Employee (emp1): "); 

    scanf (" %d", &ptr1->id); 

    printf (" Enter the age of the Employee (emp1): "); 

    scanf (" %d", &ptr1->age); 

    printf (" Enter the gender of the Employee (emp1): "); 

    scanf (" %s", &ptr1->gender); 

    printf (" Enter the city of the Employee (emp1): "); 

    scanf (" %s", &ptr1->city); 

    printf (" \n Second Employee: \n"); 

            printf (" Enter the name of the Employee (emp2): "); 

    scanf (" %s", &ptr2->name); 

    printf (" Enter the id of the Employee (emp2): "); 

    scanf (" %d", &ptr2->id); 

    printf (" Enter the age of the Employee (emp2): "); 

    scanf (" %d", &ptr2->age); 

    printf (" Enter the gender of the Employee (emp2): "); 

    scanf (" %s", &ptr2->gender); 

    printf (" Enter the city of the Employee (emp2): "); 

    scanf (" %s", &ptr2->city); 

    printf ("\n Display the Details of the Employee using Structure Pointer"); 

    printf ("\n Details of the Employee (emp1) \n"); 

    printf(" Name: %s\n", ptr1->name); 

    printf(" Id: %d\n", ptr1->id); 

    printf(" Age: %d\n", ptr1->age); 

    printf(" Gender: %s\n", ptr1->gender); 

    printf(" City: %s\n", ptr1->city); 

    printf ("\n Details of the Employee (emp2) \n"); 

    printf(" Name: %s\n", ptr2->name); 

    printf(" Id: %d\n", ptr2->id); 

    printf(" Age: %d\n", ptr2->age); 

    printf(" Gender: %s\n", ptr2->gender); 

    printf(" City: %s\n", ptr2->city); 

    return 0; 

}  

Output:

Enter the name of the Employee (emp1): John

Enter the id of the Employee (emp1): 1099

Enter the age of the Employee (emp1): 28

Enter the gender of the Employee (emp1): Male

Enter the city of the Employee (emp1): California

Second Employee: 

Enter the name of the Employee (emp2): Maria

Enter the id of the Employee (emp2): 1109

Enter the age of the Employee (emp2): 23

Enter the gender of the Employee (emp2): Female

Enter the city of the Employee (emp2): Los Angeles

Display the Details of the Employee using Structure Pointer

Details of the Employee (emp1)

Name: John

Id: 1099

Age: 28

Gender: Male

City: California

Details of the Employee (emp2) Name: Maria

Id: 1109

Age: 23

Gender: Female

City: Los Angeles

Q16) Write a Program to access the structure member using structure pointer and the dot operator?

A16) Consider the following example of creating a Subject structure and accessing its components with a structure pointer that points to the Subject variable's address in C.

#include <stdio.h> 

// create a structure Subject using the struct keyword 

Struct Subject 

{ 

    // declare the member of the Course structure 

    char sub_name[30]; 

    int sub_id; 

    char sub_duration[50]; 

    char sub_type[50]; 

}; 

Int main() 

{ 

    struct Subject sub; // declare the Subject variable 

    struct Subject *ptr; // create a pointer variable (*ptr)  

    ptr = ⊂ /* ptr variable pointing to the address of the structure variable sub */ 

    strcpy (sub.sub_name, " Computer Science"); 

    sub.sub_id = 1201; 

    strcpy (sub.sub_duration, "6 Months"); 

    strcpy (sub.sub_type, " Multiple Choice Question"); 

    // print the details of the Subject; 

    printf (" Subject Name: %s\t ", (*ptr).sub_name); 

            printf (" \n Subject Id: %d\t ", (*ptr).sub_id); 

        printf (" \n Duration of the Subject: %s\t ", (*ptr).sub_duration); 

           printf (" \n Type of the Subject: %s\t ", (*ptr).sub_type); 

    return 0; 

} 

Output:

Subject Name: Computer Science

Subject Id: 1201

Duration of the Subject: 6 Months

Type of the Subject: Multiple Choice Question

Q17) What is sizeof ()?

A17) In C, the sizeof() operator is frequently used. It determines the number of char-sized storage units used to store the expression or data type. The sizeof() operator has only one operand, which can either be an expression or a data typecast with the cast encapsulated in parenthesis. The data type can be pointer data types or complex data types like unions and structs, in addition to primitive data types like integer and floating data types.

Need of sizeof() operator

The storage size of basic data types is mostly known by programmes. The data type's storage size is constant, but it differs when implemented on different platforms. For example, we dynamically allocate the array space by using sizeof() operator:

Int *ptr=malloc(10*sizeof(int)); 

The sizeof() operation is applied to the cast of type int in the preceding example. The malloc() method is used to allocate memory and returns a reference to the memory that has been allocated. The memory space is calculated by multiplying the amount of bytes occupied by the int data type by ten.

Depending on the kind of operand, the sizeof() operator operates differently.

●      Operand is a data type

●      Operand is an expression

Q18) Define typedef?

A18) typedef

The typedef keyword is used in C programming to give meaningful names to variables that already exist in the programme. It works similarly to how we construct aliases for commands. In a nutshell, this keyword is used to change the name of a variable that already exists.

Syntax of typedef

Typedef <existing_name> <alias_name> 

'existing name' is the name of an already existing variable in the aforementioned syntax, while 'alias name' is another name for the same variable.

If we wish to create a variable of type unsigned int, for example, it will be a time-consuming operation if we want to declare several variables of this kind. We utilise the typedef keyword to solve the problem.

Typedef unsigned int unit; 

We used the typedef keyword to declare the unsigned int unit variable in the above statements.

By writing the following statement, we can now create variables of type unsigned int:

Unit a, b;  

Rather than writing:

Unsigned int a, b; 

So far, we've seen how the typedef keyword provides a convenient shortcut by offering an alternate name for a variable that already exists. This keyword comes in handy when working with lengthy data types, particularly structure declarations.

Example

#include <stdio.h> 

Int main() 

{ 

Typedef unsigned int unit; 

Unit i,j; 

i=10; 

j=20; 

Printf("Value of i is :%d",i); 

Printf("\nValue of j is :%d",j); 

Return 0; 

}

Output

Value of i is :10

Value of j is :20

Q19) Write notes on - fseek(), ftell() and rewind()?

A19) fseek()

To set the file pointer to a certain offset, use the fseek() function. It's used to save data to a file at a certain location.

Syntax:

Int fseek(FILE *stream, long int offset, int whence) 

Whence, the fseek() function uses three constants: SEEK SET, SEEK CUR, and SEEK END.

Example

#include <stdio.h> 

Void main(){ 

   FILE *fp; 

   fp = fopen("myfile.txt","w+"); 

   fputs("This is javatpoint", fp); 

   fseek( fp, 7, SEEK_SET ); 

   fputs("sonoo jaiswal", fp); 

   fclose(fp); 

} 

Output

This is sonam jaiswal

Ftell()

The ftell() function returns the supplied stream's current file position. After shifting the file pointer to the end of the file, we can use the ftell() function to retrieve the total size of the file. The SEEK END constant can be used to relocate the file pointer to the end of the file.

Syntax:

Long int ftell(FILE *stream) 

Example

#include <stdio.h> 

#include <conio.h> 

Void main (){ 

   FILE *fp; 

   int length; 

   clrscr(); 

   fp = fopen("file.txt", "r"); 

   fseek(fp, 0, SEEK_END); 

   length = ftell(fp); 

   fclose(fp); 

   printf("Size of file: %d bytes", length); 

   getch(); 

} 

Output:

Size of file: 21 bytes

Rewind()

The file pointer is set to the beginning of the stream using the rewind() function. It's useful if you'll be using stream frequently.

Syntax:

Void rewind(FILE *stream) 

Example

#include<stdio.h> 

#include<conio.h> 

Void main(){ 

FILE *fp; 

Char c; 

Clrscr(); 

Fp=fopen("file.txt","r"); 

While((c=fgetc(fp))!=EOF){ 

Printf("%c",c); 

} 

Rewind(fp);//moves the file pointer at beginning of the file 

While((c=fgetc(fp))!=EOF){ 

Printf("%c",c); 

} 

Fclose(fp);   

Getch();   

}   

Output:

This is a simple textthis is a simple text

The rewind() function, as you can see, moves the file pointer to the beginning of the file, which is why "this is simple text" is printed twice. If the rewind() function is not used, "this is simple text" will only be printed once.

Q20) What are the formatted input?

A20) scanf()

We utilize the scanf() function to get formatted or standard inputs so that the printf() function can give the programme a variety of conversion possibilities.

Syntax for scanf()

Scanf (format_specifier, &data_a, &data_b,……); // Here, & refers to the address operator

The scanf() function's goal is to read the characters from the standard input, convert them according to the format string, and then store the accessible inputs in the memory slots represented by the other arguments.

Example of scanf()

Scanf(“%d %c”, &info_a,&info_b);

The '&' character does not preface the data name when considering string data names in a programme.

Sscanf()

Int sscanf(const char *str, const char *format,...) is a C function that reads formatted input from a string.

Declaration

The sscanf() function is declared as follows.

Int sscanf(const char *str, const char *format, ...)

Parameters

●      str - This is the C string that the function uses as its data source.

●      format - is a C string that contains one or more of the items listed below: Format specifiers, whitespace characters, and non-whitespace characters

This prototype is followed by a format specifier: [=%[*] [width] [modifiers]type=]

Fscanf()

To read a collection of characters from a file, use the fscanf() method. It reads a single word from the file and returns EOF when the file reaches the end.

Syntax:

Int fscanf(FILE *stream, const char *format [, argument, ...]) 

Example:

#include <stdio.h> 

Main(){ 

   FILE *fp; 

   char buff[255];//creating char array to store data of file 

   fp = fopen("file.txt", "r"); 

   while(fscanf(fp, "%s", buff)!=EOF){ 

   printf("%s ", buff ); 

   } 

   fclose(fp); 

} 

Output:

Hello file by fprintf...

Fread()

The fread() function is the fwrite() function's counterpart. To read binary data, the fread() function is widely used. It takes the same parameters as the fwrite() function. The fread() method has the following syntax:

Syntax:

Size_t fread(void *ptr, size_t size, size_t n, FILE *fp);

After reading from the file, the ptr is the starting address of the RAM block where data will be stored. The function reads n items from the file, each of which takes up the amount of bytes indicated in the second argument. It reads n items from the file and returns n if it succeeds. It returns a number smaller than n in the event of an error or the end of the file.

Example

Reading a structure array

Struct student

{

    char name[10];

    int roll;

    float marks;

};

Struct student arr_student[100];

Fread(&arr_student, sizeof(struct student), 10, fp);

This reads the first 10 struct student elements from the file and places them in the arr_studen variable.

Unit - 2

Structures, Union and File Handling

Q1) Define structure? Explain how to access elements in structures?

A1) Structure

A structure can be considered as a template used for defining a collection of variables under a single name. Structures help programmers to group elements of different data types into a single logical unit (Unlike arrays which permit a programmer to group only elements of same data type).

Why Use Structures

•         Ordinary variables can hold one piece of information

•         arrays can hold a number of pieces of information of the same data type.

For example, suppose you want to store data about a book. You might want to  store its name (a string), its price (a float) and number of pages in it (an int).

If data about say 3 such books is to be stored, then we can follow two approaches:

• Construct individual arrays, one for storing names, another for storing prices and still another for storing number of pages.
• Use a structure variable.

Suppose we want to create a employee database. Then, we can define a structure called employee with three elements id, name and salary. The syntax of this structure is as follows:

Struct employee

{   int id;

Char name[50];

Float salary;

};

Q2) Explain structure variable declaration?

A2) Structure variable

We can declare the variable of structure in two ways

1. Declare the structure inside main function
2. Declare the structure outside the main function.

1. Declare the structure inside main function

Following example show you, how structure variable is declared inside main function

Struct employee

{

Int id;

Char name[50];

Float salary;

};

Int main()

{

Struct employee e1, e2;

Return 0;

}

In this example the variable of structure employee is created inside main function that e1 ,e2.

2. Declare the structure outside main function

Following example show you, how structure variable is declared outside the main function

Struct employee

{

Int id;

Char name[50];

Float salary;

}e1,e2;

Q3) How do you declare structures for multiple variables?

A3) Declaration

Struct student

{

Char name[20];

Int roll;

Float marks;

}

Std1 = {"Poonam" ,67, 78.3};

Std2 = {"Vishal",62, 71.3};

In this example, we have declared two structure variables in above code. After declaration of variable we have initialized two variable.

Std1 = {"Poonam" ,67, 78.3};

Std2 = {"Vishal",62, 71.3};

Q4) How do you access structure elements in the array?

A4) Access structure element in array

Structure is a collection of different data types. An object of structure represents a single record in memory, if we want more than one record of structure type, we have to create an array of structure or object. As we know, an array is a collection of similar type, therefore an array can be of structure type.

Syntax for declaring structure array

Struct struct-name

{

Datatype var1;

Datatype var2;

- - - - - - - - - -

- - - - - - - - - -

Datatype varN;

};

Struct struct-name obj [ size ];

Example for declaring structure array

#include<stdio.h>

Struct Employee

{

Int Id;

Char Name[25];

Int Age;

Long Salary;

};

Void main()

{

Int i;

Struct Employee Emp[ 3 ]; //Statement 1

For(i=0;i<3;i++)

{

Printf("\nEnter details of %d Employee",i+1);

Printf("\n\tEnter Employee Id : ");

Scanf("%d",&Emp[i].Id);

Printf("\n\tEnter Employee Name : ");

Scanf("%s",&Emp[i].Name);

Printf("\n\tEnter Employee Age : ");

Scanf("%d",&Emp[i].Age);

Printf("\n\tEnter Employee Salary : ");

Scanf("%ld",&Emp[i].Salary);

}

Printf("\nDetails of Employees");

For(i=0;i<3;i++)

Printf("\n%d\t%s\t%d\t%ld",Emp[i].Id,Emp[i].Name,Emp[i].Age,Emp[i].Salary);

}

Output:

Enter details of 1 Employee

Enter Employee Id : 101

Enter Employee Name : Suresh

Enter Employee Age : 29

Enter Employee Salary : 45000

Enter details of 2 Employee

Enter Employee Id : 102

Enter Employee Name : Mukesh

Enter Employee Age : 31

Enter Employee Salary : 51000

Enter details of 3 Employee

Enter Employee Id : 103

Enter Employee Name : Ramesh

Enter Employee Age : 28

Enter Employee Salary : 47000

Details of Employees

101 Suresh 29 45000

102 Mukesh 31 51000

103 Ramesh 28 47000

In the above example, we are getting and displaying the data of 3 employee using array of object. Statement 1 is creating an array of Employee Emp to store the records of 3 employees.

Array within Structure

As we know, structure is collection of different data type. Like normal data type, It can

Also store an array as well.

Syntax for array within structure

Struct struct-name

{

Datatype var1; // normal variable

Datatype array [size]; // array variable

- - - - - - - - - -

- - - - - - - - - -

Datatype varN;

};

Struct struct-name obj;

Example for array within structure

Struct Student

{

Int Roll;

Char Name[25];

Int Marks[3]; //Statement 1 : array of marks

Int Total;

Float Avg;

};

Void main()

{

Int i;

Struct Student S;

Printf("\n\nEnter Student Roll : ");

Scanf("%d",&S.Roll);

Printf("\n\nEnter Student Name : ");

Scanf("%s",&S.Name);

S.Total = 0;

For(i=0;i<3;i++)

{

Printf("\n\nEnter Marks %d : ",i+1);

Scanf("%d",&S.Marks[i]);

S.Total = S.Total + S.Marks[i];

}

S.Avg = S.Total / 3;

Printf("\nRoll : %d",S.Roll);

Printf("\nName : %s",S.Name);

Printf("\nTotal : %d",S.Total);

Printf("\nAverage : %f",S.Avg);

}

Output:

Enter Student Roll : 10

Enter Student Name : Kumar

Enter Marks 1 : 78

Enter Marks 2 : 89

Enter Marks 3 : 56

Roll : 10

Name : Kumar

Total : 223

Average: 74.00000

In the above example, we have created an array Marks[ ] inside structure representing 3 marks of a single student. Marks[ ] is now a member of structure student and to access Marks[ ] we have used dot operator(.) along with object S.

Q5) Write a program to obtain the details of the 3 employees?

A5) Program

#include <iostream>

Using namespace std;

Struct employee {

String ename;

Int age, phn_no;

Int salary;

};

// Function to display details of all employees

Void display(struct employee emp[], int n)

{

Cout<< "Name\tAge\tPhone Number\tSalary\n";

For (int i = 0; i< n; i++) {

Cout<< emp[i].ename<< "\t" << emp[i].age << "\t"

<< emp[i].phn_no<< "\t" << emp[i].salary << "\n";

}

}

// Driver code

Int main()

{

Int n = 3;

// Array of structure objects

Struct employee emp[n];

// Details of employee 1

Emp[0].ename = "Chirag";

Emp[0].age = 24;

Emp[0].phn_no = 1234567788;

Emp[0].salary = 20000;

// Details of employee 2

Emp[1].ename = "Arnav";

Emp[1].age = 31;

Emp[1].phn_no = 1234567891;

Emp[1].salary = 56000;

// Details of employee 3

Emp[2].ename = "Shivam";

Emp[2].age = 45;

Emp[2].phn_no = 1100661111;

Emp[2].salary = 30500;

Display(emp, n);

Return 0;

}

Output:

Name     Age    Phone Number   Salary

Chirag   24     1234567788      20000

Arnav    31     1234567891      56000

Shivam   45     8881101111      30500

Q6) Define union?

A6) Union

Unions are quite similar to the structures in C. Union is also a derived type as structure. Union can be defined in same manner as structures just the keyword used in defining union in union where keyword used in defining structure was struct.

Union car

{

Char name[50];

Int price;

};

Union variables can be created in similar manner as structure variable.

Union car

{

Char name[50];

Int price;

}c1, c2, *c3;

OR;

Union car

{

Char name[50];

Int price;

};

-------Inside Function-----------

Union car c1, c2, *c3;

In both cases, union variables c1, c2 and union pointer variable c3 of type union car is created.

Q7) How do you access the members of the union?

A7) Access member of union

●       Array elements are accessed using the Subscript variable , Similarly Union members are accessed using dot [.] operator.

●       (.) is called as “union member Operator”.

●       Use this Operator in between “Union variable”&“member name”

Union employee

{

Int id;

Char name[50];

Float salary;

} ;

Void main()

{

Union employee e1= { 1, “ABC”, 50000 };

Printf(“%d”, e. Id);

Printf(“%s”, e. Name);

}

O/P-  garbage value, ABC

Q8) Compare structure and union?

A8) Structure Vs Union

Q9) Write a program to store information of students and display it?

A9) Program

#include <stdio.h>

#include <string.h>

Union Student

{

Int age;

Char Name[50];

Char Department[20];

};

Int main()

{

Union student stud1;

Union Employee stud2;

Stud1.age = 28;

Strcpy(stud1.Name, "Chris");

Strcpy(stud1.Department, "Science");

Printf("\nDetails of the First Student \n");

Printf("  Student Age = %d \n", emp1.age);

Printf("  Student Name = %s \n", emp1.Name);

Printf("  Student Department = %s \n", emp1.Department);

Printf("Details of the Second Student \n" );

Stud2.age = 30;

Printf("  Student Age = %d \n", stud2.age );

Strcpy(stud2.Name, "David");

Printf("  Student Name = %s \n", stud2.Name );

Strcpy(stud2.Department, "Technology" );

Printf("  Student Department = %s \n ", stud2.Department );

Return 0;

}

OUTPUT:

Details of the first student

Student Age = 28

Student Name = Chris

Student Department = Science

Details of the Second Student

Student Age =30

Student Name = David

Student Department= Technology

Q10) Write the advantages and disadvantages of structure?

A10) Advantages of structure

●       Structures gather more than one piece of data about the same subject together in the same place.

●       It is helpful when you want to gather the data of similar data types and parameters like first name, last name, etc.

●       It is very easy to maintain as we can represent the whole record by using a single name.

●       In structure, we can pass a complete set of records to any function using a single parameter.

●       You can use an array of structure to store more records with similar types.

Disadvantages of structure

●       If the complexity of an IT project goes beyond the limit, it becomes hard to manage.

●       Change of one data structure in a code necessitates changes at many other places. Therefore, the changes become hard to track.

●       Structure is slower because it requires storage space for all the data.

●       You can retrieve any member at a time in structure whereas you can access one member at a time in the union.

●       Structure occupies space for each and every member written in inner parameters while union occupies space for a member having the highest size written in inner parameters.

●       Structure supports a flexible array. Union does not support a flexible array.

Q11) Write an example for calloc ()?

A11) Program

Example of calloc()

#include<stdio.h>

#include<stdlib.h>

Int main()

{

Int n,i,*ptr,sum=0;

Printf("Enter number of elements: ");

Scanf("%d",&n);

Ptr=(int*)calloc(n,sizeof(int));  //memory allocated using calloc

If(ptr==NULL)

{

Printf("Sorry! unable to allocate memory");

Exit(0);

}

Printf("Enter elements of array: ");

For(i=0;i<n;++i)

{

Scanf("%d",ptr+i);

Sum+=*(ptr+i);

}

Printf("Sum=%d",sum);

Free(ptr);

Return 0;

}

Output

Enter elements of array: 3

Enter elements of array: 10

10

10

Sum=30

Q12) Explain nested structure?

A12) The feature of nesting one structure within another structure in C allows us to design complicated data types. For example, we could need to keep an entity employee's address in a structure. Street number, city, state, and pin code are all possible subparts of the attribute address. As a result, we must store the employee's address in a different structure and nest the structure address into the structure employee to store the employee's address.

In the following methods, the structure can be nested.

●      By separate structure

●      By Embedded structure

1) Separate structure

We've created two structures here, but the dependent structure should be utilised as a member inside the primary structure. Consider the following illustration.

Struct Date 

{ 

   int dd; 

   int mm; 

   int yyyy;  

}; 

Struct Employee 

{    

   int id; 

   char name[20]; 

   struct Date doj; 

}emp1; 

Doj (date of joining) is a Date variable, as you can see. In this case, doj is a member of the Employee structure. We may utilise the Date structure in a variety of structures this way.

2) Embedded structure

We can declare the structure inside the structure using the embedded structure. As a result, it uses fewer lines of code, but it cannot be applied to numerous data structures. Consider the following illustration.

Struct Employee 

{    

   int id; 

   char name[20]; 

   struct Date 

    { 

      int dd; 

      int mm; 

      int yyyy;  

    }doj; 

}emp1; 

Accessing Nested Structure

We can access the member of the nested structure by

Outer_Structure.Nested_Structure.member as given below:

e1.doj.dd 

e1.doj.mm

e1.doj.yyyy 

Example of Nested Structure

#include <stdio.h> 

#include <string.h> 

Struct Employee 

{    

   int id; 

   char name[20]; 

   struct Date 

    { 

      int dd; 

      int mm; 

      int yyyy;  

    }doj; 

}e1; 

Int main( ) 

{ 

   //storing employee information 

   e1.id=101; 

   strcpy(e1.name, "Sonoo Jaiswal");//copying string into char array 

   e1.doj.dd=10; 

   e1.doj.mm=11; 

   e1.doj.yyyy=2014; 

   //printing first employee information 

   printf( "employee id : %d\n", e1.id); 

   printf( "employee name : %s\n", e1.name); 

   printf( "employee date of joining (dd/mm/yyyy) : %d/%d/%d\n", e1.doj.dd,e1.doj.mm,e1.doj.yyyy); 

   return 0; 

}

Output:

Employee id : 101

Employee name : Sonoo Jaiswal

Employee date of joining (dd/mm/yyyy) : 10/11/2014

Q13) Write a program for nested strcuture?

A13) Consider the programme below.

#include<stdio.h> 

Struct address  

{ 

    char city[20]; 

    int pin; 

    char phone[14]; 

}; 

Struct employee 

{ 

    char name[20]; 

    struct address add; 

}; 

Void main () 

{ 

    struct employee emp; 

    printf("Enter employee information?\n"); 

    scanf("%s %s %d %s",emp.name,emp.add.city, &emp.add.pin, emp.add.phone); 

    printf("Printing the employee information....\n"); 

    printf("name: %s\nCity: %s\nPincode: %d\nPhone: %s",emp.name,emp.add.city,emp.add.pin,emp.add.phone); 

} 

Output

Enter employee information?

Arun           

Delhi          

110001      

1234567890   

Printing the employee information....  

Name: Arun     

City: Delhi 

Pincode: 110001

Phone: 1234567890

Q14) Describe an Array of structure with an example?

A14) In C, an array of structures is a collection of many structure variables, each of which contains information on a different entity. In C, an array of structures is used to store data about many entities of various data kinds. The collection of structures is another name for the array of structures.

Fig 1: Array of structure

Let's look at an array of structures that stores and outputs information for five students.

#include<stdio.h> 

#include <string.h>   

Struct student{   

Int rollno;   

Char name[10];   

};   

Int main(){   

Int i;   

Struct student st[5];   

Printf("Enter Records of 5 students");   

For(i=0;i<5;i++){   

Printf("\nEnter Rollno:");   

Scanf("%d",&st[i].rollno);   

Printf("\nEnter Name:");   

Scanf("%s",&st[i].name);   

}   

Printf("\nStudent Information List:");   

For(i=0;i<5;i++){   

Printf("\nRollno:%d, Name:%s",st[i].rollno,st[i].name);   

}   

   return 0;   

}  

Output:

Enter Records of 5 students

Enter Rollno:10

Enter Name:Sonu

Enter Rollno:20

Enter Name:Ratana

Enter Rollno:30

Enter Name:Vomika

Enter Rollno:40

Enter Name:James

Enter Rollno:50

Enter Name:Sadaf

Student Information List:

Rollno:10, Name:Sonu

Rollno:20, Name:Ratanaa

Rollno:30, Name:Vomika

Rollno:40, Name:James

Rollno:50, Name:Sadaf

Q15) Write a Program to access the structure member using the structure pointer and arrow (->) operator?

A15) Consider a C programme that uses the pointer and the arrow (->) operator to access structure members.

#include <stdio.h>

// create Employee structure  

Struct Employee 

{ 

    // define the member of the structure 

    char name[30]; 

    int id; 

    int age; 

    char gender[30]; 

    char city[40]; 

}; 

// define the variables of the Structure with pointers 

Struct Employee emp1, emp2, *ptr1, *ptr2; 

Int main() 

{ 

    // store the address of the emp1 and emp2 structure variable 

    ptr1 = &emp1; 

    ptr2 = &emp2; 

    printf (" Enter the name of the Employee (emp1): "); 

    scanf (" %s", &ptr1->name); 

    printf (" Enter the id of the Employee (emp1): "); 

    scanf (" %d", &ptr1->id); 

    printf (" Enter the age of the Employee (emp1): "); 

    scanf (" %d", &ptr1->age); 

    printf (" Enter the gender of the Employee (emp1): "); 

    scanf (" %s", &ptr1->gender); 

    printf (" Enter the city of the Employee (emp1): "); 

    scanf (" %s", &ptr1->city); 

    printf (" \n Second Employee: \n"); 

            printf (" Enter the name of the Employee (emp2): "); 

    scanf (" %s", &ptr2->name); 

    printf (" Enter the id of the Employee (emp2): "); 

    scanf (" %d", &ptr2->id); 

    printf (" Enter the age of the Employee (emp2): "); 

    scanf (" %d", &ptr2->age); 

    printf (" Enter the gender of the Employee (emp2): "); 

    scanf (" %s", &ptr2->gender); 

    printf (" Enter the city of the Employee (emp2): "); 

    scanf (" %s", &ptr2->city); 

    printf ("\n Display the Details of the Employee using Structure Pointer"); 

    printf ("\n Details of the Employee (emp1) \n"); 

    printf(" Name: %s\n", ptr1->name); 

    printf(" Id: %d\n", ptr1->id); 

    printf(" Age: %d\n", ptr1->age); 

    printf(" Gender: %s\n", ptr1->gender); 

    printf(" City: %s\n", ptr1->city); 

    printf ("\n Details of the Employee (emp2) \n"); 

    printf(" Name: %s\n", ptr2->name); 

    printf(" Id: %d\n", ptr2->id); 

    printf(" Age: %d\n", ptr2->age); 

    printf(" Gender: %s\n", ptr2->gender); 

    printf(" City: %s\n", ptr2->city); 

    return 0; 

}  

Output:

Enter the name of the Employee (emp1): John

Enter the id of the Employee (emp1): 1099

Enter the age of the Employee (emp1): 28

Enter the gender of the Employee (emp1): Male

Enter the city of the Employee (emp1): California

Second Employee: 

Enter the name of the Employee (emp2): Maria

Enter the id of the Employee (emp2): 1109

Enter the age of the Employee (emp2): 23

Enter the gender of the Employee (emp2): Female

Enter the city of the Employee (emp2): Los Angeles

Display the Details of the Employee using Structure Pointer

Details of the Employee (emp1)

Name: John

Id: 1099

Age: 28

Gender: Male

City: California

Details of the Employee (emp2) Name: Maria

Id: 1109

Age: 23

Gender: Female

City: Los Angeles

Q16) Write a Program to access the structure member using structure pointer and the dot operator?

A16) Consider the following example of creating a Subject structure and accessing its components with a structure pointer that points to the Subject variable's address in C.

#include <stdio.h> 

// create a structure Subject using the struct keyword 

Struct Subject 

{ 

    // declare the member of the Course structure 

    char sub_name[30]; 

    int sub_id; 

    char sub_duration[50]; 

    char sub_type[50]; 

}; 

Int main() 

{ 

    struct Subject sub; // declare the Subject variable 

    struct Subject *ptr; // create a pointer variable (*ptr)  

    ptr = ⊂ /* ptr variable pointing to the address of the structure variable sub */ 

    strcpy (sub.sub_name, " Computer Science"); 

    sub.sub_id = 1201; 

    strcpy (sub.sub_duration, "6 Months"); 

    strcpy (sub.sub_type, " Multiple Choice Question"); 

    // print the details of the Subject; 

    printf (" Subject Name: %s\t ", (*ptr).sub_name); 

            printf (" \n Subject Id: %d\t ", (*ptr).sub_id); 

        printf (" \n Duration of the Subject: %s\t ", (*ptr).sub_duration); 

           printf (" \n Type of the Subject: %s\t ", (*ptr).sub_type); 

    return 0; 

} 

Output:

Subject Name: Computer Science

Subject Id: 1201

Duration of the Subject: 6 Months

Type of the Subject: Multiple Choice Question

Q17) What is sizeof ()?

A17) In C, the sizeof() operator is frequently used. It determines the number of char-sized storage units used to store the expression or data type. The sizeof() operator has only one operand, which can either be an expression or a data typecast with the cast encapsulated in parenthesis. The data type can be pointer data types or complex data types like unions and structs, in addition to primitive data types like integer and floating data types.

Need of sizeof() operator

The storage size of basic data types is mostly known by programmes. The data type's storage size is constant, but it differs when implemented on different platforms. For example, we dynamically allocate the array space by using sizeof() operator:

Int *ptr=malloc(10*sizeof(int)); 

The sizeof() operation is applied to the cast of type int in the preceding example. The malloc() method is used to allocate memory and returns a reference to the memory that has been allocated. The memory space is calculated by multiplying the amount of bytes occupied by the int data type by ten.

Depending on the kind of operand, the sizeof() operator operates differently.

●      Operand is a data type

●      Operand is an expression

Q18) Define typedef?

A18) typedef

The typedef keyword is used in C programming to give meaningful names to variables that already exist in the programme. It works similarly to how we construct aliases for commands. In a nutshell, this keyword is used to change the name of a variable that already exists.

Syntax of typedef

Typedef <existing_name> <alias_name> 

'existing name' is the name of an already existing variable in the aforementioned syntax, while 'alias name' is another name for the same variable.

If we wish to create a variable of type unsigned int, for example, it will be a time-consuming operation if we want to declare several variables of this kind. We utilise the typedef keyword to solve the problem.

Typedef unsigned int unit; 

We used the typedef keyword to declare the unsigned int unit variable in the above statements.

By writing the following statement, we can now create variables of type unsigned int:

Unit a, b;  

Rather than writing:

Unsigned int a, b; 

So far, we've seen how the typedef keyword provides a convenient shortcut by offering an alternate name for a variable that already exists. This keyword comes in handy when working with lengthy data types, particularly structure declarations.

Example

#include <stdio.h> 

Int main() 

{ 

Typedef unsigned int unit; 

Unit i,j; 

i=10; 

j=20; 

Printf("Value of i is :%d",i); 

Printf("\nValue of j is :%d",j); 

Return 0; 

}

Output

Value of i is :10

Value of j is :20

Q19) Write notes on - fseek(), ftell() and rewind()?

A19) fseek()

To set the file pointer to a certain offset, use the fseek() function. It's used to save data to a file at a certain location.

Syntax:

Int fseek(FILE *stream, long int offset, int whence) 

Whence, the fseek() function uses three constants: SEEK SET, SEEK CUR, and SEEK END.

Example

#include <stdio.h> 

Void main(){ 

   FILE *fp; 

   fp = fopen("myfile.txt","w+"); 

   fputs("This is javatpoint", fp); 

   fseek( fp, 7, SEEK_SET ); 

   fputs("sonoo jaiswal", fp); 

   fclose(fp); 

} 

Output

This is sonam jaiswal

Ftell()

The ftell() function returns the supplied stream's current file position. After shifting the file pointer to the end of the file, we can use the ftell() function to retrieve the total size of the file. The SEEK END constant can be used to relocate the file pointer to the end of the file.

Syntax:

Long int ftell(FILE *stream) 

Example

#include <stdio.h> 

#include <conio.h> 

Void main (){ 

   FILE *fp; 

   int length; 

   clrscr(); 

   fp = fopen("file.txt", "r"); 

   fseek(fp, 0, SEEK_END); 

   length = ftell(fp); 

   fclose(fp); 

   printf("Size of file: %d bytes", length); 

   getch(); 

} 

Output:

Size of file: 21 bytes

Rewind()

The file pointer is set to the beginning of the stream using the rewind() function. It's useful if you'll be using stream frequently.

Syntax:

Void rewind(FILE *stream) 

Example

#include<stdio.h> 

#include<conio.h> 

Void main(){ 

FILE *fp; 

Char c; 

Clrscr(); 

Fp=fopen("file.txt","r"); 

While((c=fgetc(fp))!=EOF){ 

Printf("%c",c); 

} 

Rewind(fp);//moves the file pointer at beginning of the file 

While((c=fgetc(fp))!=EOF){ 

Printf("%c",c); 

} 

Fclose(fp);   

Getch();   

}   

Output:

This is a simple textthis is a simple text

The rewind() function, as you can see, moves the file pointer to the beginning of the file, which is why "this is simple text" is printed twice. If the rewind() function is not used, "this is simple text" will only be printed once.

Q20) What are the formatted input?

A20) scanf()

We utilize the scanf() function to get formatted or standard inputs so that the printf() function can give the programme a variety of conversion possibilities.

Syntax for scanf()

Scanf (format_specifier, &data_a, &data_b,……); // Here, & refers to the address operator

The scanf() function's goal is to read the characters from the standard input, convert them according to the format string, and then store the accessible inputs in the memory slots represented by the other arguments.

Example of scanf()

Scanf(“%d %c”, &info_a,&info_b);

The '&' character does not preface the data name when considering string data names in a programme.

Sscanf()

Int sscanf(const char *str, const char *format,...) is a C function that reads formatted input from a string.

Declaration

The sscanf() function is declared as follows.

Int sscanf(const char *str, const char *format, ...)

Parameters

●      str - This is the C string that the function uses as its data source.

●      format - is a C string that contains one or more of the items listed below: Format specifiers, whitespace characters, and non-whitespace characters

This prototype is followed by a format specifier: [=%[*] [width] [modifiers]type=]

Fscanf()

To read a collection of characters from a file, use the fscanf() method. It reads a single word from the file and returns EOF when the file reaches the end.

Syntax:

Int fscanf(FILE *stream, const char *format [, argument, ...]) 

Example:

#include <stdio.h> 

Main(){ 

   FILE *fp; 

   char buff[255];//creating char array to store data of file 

   fp = fopen("file.txt", "r"); 

   while(fscanf(fp, "%s", buff)!=EOF){ 

   printf("%s ", buff ); 

   } 

   fclose(fp); 

} 

Output:

Hello file by fprintf...

Fread()

The fread() function is the fwrite() function's counterpart. To read binary data, the fread() function is widely used. It takes the same parameters as the fwrite() function. The fread() method has the following syntax:

Syntax:

Size_t fread(void *ptr, size_t size, size_t n, FILE *fp);

After reading from the file, the ptr is the starting address of the RAM block where data will be stored. The function reads n items from the file, each of which takes up the amount of bytes indicated in the second argument. It reads n items from the file and returns n if it succeeds. It returns a number smaller than n in the event of an error or the end of the file.

Example

Reading a structure array

Struct student

{

    char name[10];

    int roll;

    float marks;

};

Struct student arr_student[100];

Fread(&arr_student, sizeof(struct student), 10, fp);

This reads the first 10 struct student elements from the file and places them in the arr_studen variable.

Unit - 2

Structures, Union and File Handling

Q1) Define structure? Explain how to access elements in structures?

A1) Structure

A structure can be considered as a template used for defining a collection of variables under a single name. Structures help programmers to group elements of different data types into a single logical unit (Unlike arrays which permit a programmer to group only elements of same data type).

Why Use Structures

•         Ordinary variables can hold one piece of information

•         arrays can hold a number of pieces of information of the same data type.

For example, suppose you want to store data about a book. You might want to  store its name (a string), its price (a float) and number of pages in it (an int).

If data about say 3 such books is to be stored, then we can follow two approaches:

• Construct individual arrays, one for storing names, another for storing prices and still another for storing number of pages.
• Use a structure variable.

Suppose we want to create a employee database. Then, we can define a structure called employee with three elements id, name and salary. The syntax of this structure is as follows:

Struct employee

{   int id;

Char name[50];

Float salary;

};

Q2) Explain structure variable declaration?

A2) Structure variable

We can declare the variable of structure in two ways

1. Declare the structure inside main function
2. Declare the structure outside the main function.

1. Declare the structure inside main function

Following example show you, how structure variable is declared inside main function

Struct employee

{

Int id;

Char name[50];

Float salary;

};

Int main()

{

Struct employee e1, e2;

Return 0;

}

In this example the variable of structure employee is created inside main function that e1 ,e2.

2. Declare the structure outside main function

Following example show you, how structure variable is declared outside the main function

Struct employee

{

Int id;

Char name[50];

Float salary;

}e1,e2;

Q3) How do you declare structures for multiple variables?

A3) Declaration

Struct student

{

Char name[20];

Int roll;

Float marks;

}

Std1 = {"Poonam" ,67, 78.3};

Std2 = {"Vishal",62, 71.3};

In this example, we have declared two structure variables in above code. After declaration of variable we have initialized two variable.

Std1 = {"Poonam" ,67, 78.3};

Std2 = {"Vishal",62, 71.3};

Q4) How do you access structure elements in the array?

A4) Access structure element in array

Structure is a collection of different data types. An object of structure represents a single record in memory, if we want more than one record of structure type, we have to create an array of structure or object. As we know, an array is a collection of similar type, therefore an array can be of structure type.

Syntax for declaring structure array

Struct struct-name

{

Datatype var1;

Datatype var2;

- - - - - - - - - -

- - - - - - - - - -

Datatype varN;

};

Struct struct-name obj [ size ];

Example for declaring structure array

#include<stdio.h>

Struct Employee

{

Int Id;

Char Name[25];

Int Age;

Long Salary;

};

Void main()

{

Int i;

Struct Employee Emp[ 3 ]; //Statement 1

For(i=0;i<3;i++)

{

Printf("\nEnter details of %d Employee",i+1);

Printf("\n\tEnter Employee Id : ");

Scanf("%d",&Emp[i].Id);

Printf("\n\tEnter Employee Name : ");

Scanf("%s",&Emp[i].Name);

Printf("\n\tEnter Employee Age : ");

Scanf("%d",&Emp[i].Age);

Printf("\n\tEnter Employee Salary : ");

Scanf("%ld",&Emp[i].Salary);

}

Printf("\nDetails of Employees");

For(i=0;i<3;i++)

Printf("\n%d\t%s\t%d\t%ld",Emp[i].Id,Emp[i].Name,Emp[i].Age,Emp[i].Salary);

}

Output:

Enter details of 1 Employee

Enter Employee Id : 101

Enter Employee Name : Suresh

Enter Employee Age : 29

Enter Employee Salary : 45000

Enter details of 2 Employee

Enter Employee Id : 102

Enter Employee Name : Mukesh

Enter Employee Age : 31

Enter Employee Salary : 51000

Enter details of 3 Employee

Enter Employee Id : 103

Enter Employee Name : Ramesh

Enter Employee Age : 28

Enter Employee Salary : 47000

Details of Employees

101 Suresh 29 45000

102 Mukesh 31 51000

103 Ramesh 28 47000

In the above example, we are getting and displaying the data of 3 employee using array of object. Statement 1 is creating an array of Employee Emp to store the records of 3 employees.

Array within Structure

As we know, structure is collection of different data type. Like normal data type, It can

Also store an array as well.

Syntax for array within structure

Struct struct-name

{

Datatype var1; // normal variable

Datatype array [size]; // array variable

- - - - - - - - - -

- - - - - - - - - -

Datatype varN;

};

Struct struct-name obj;

Example for array within structure

Struct Student

{

Int Roll;

Char Name[25];

Int Marks[3]; //Statement 1 : array of marks

Int Total;

Float Avg;

};

Void main()

{

Int i;

Struct Student S;

Printf("\n\nEnter Student Roll : ");

Scanf("%d",&S.Roll);

Printf("\n\nEnter Student Name : ");

Scanf("%s",&S.Name);

S.Total = 0;

For(i=0;i<3;i++)

{

Printf("\n\nEnter Marks %d : ",i+1);

Scanf("%d",&S.Marks[i]);

S.Total = S.Total + S.Marks[i];

}

S.Avg = S.Total / 3;

Printf("\nRoll : %d",S.Roll);

Printf("\nName : %s",S.Name);

Printf("\nTotal : %d",S.Total);

Printf("\nAverage : %f",S.Avg);

}

Output:

Enter Student Roll : 10

Enter Student Name : Kumar

Enter Marks 1 : 78

Enter Marks 2 : 89

Enter Marks 3 : 56

Roll : 10

Name : Kumar

Total : 223

Average: 74.00000

In the above example, we have created an array Marks[ ] inside structure representing 3 marks of a single student. Marks[ ] is now a member of structure student and to access Marks[ ] we have used dot operator(.) along with object S.

Q5) Write a program to obtain the details of the 3 employees?

A5) Program

#include <iostream>

Using namespace std;

Struct employee {

String ename;

Int age, phn_no;

Int salary;

};

// Function to display details of all employees

Void display(struct employee emp[], int n)

{

Cout<< "Name\tAge\tPhone Number\tSalary\n";

For (int i = 0; i< n; i++) {

Cout<< emp[i].ename<< "\t" << emp[i].age << "\t"

<< emp[i].phn_no<< "\t" << emp[i].salary << "\n";

}

}

// Driver code

Int main()

{

Int n = 3;

// Array of structure objects

Struct employee emp[n];

// Details of employee 1

Emp[0].ename = "Chirag";

Emp[0].age = 24;

Emp[0].phn_no = 1234567788;

Emp[0].salary = 20000;

// Details of employee 2

Emp[1].ename = "Arnav";

Emp[1].age = 31;

Emp[1].phn_no = 1234567891;

Emp[1].salary = 56000;

// Details of employee 3

Emp[2].ename = "Shivam";

Emp[2].age = 45;

Emp[2].phn_no = 1100661111;

Emp[2].salary = 30500;

Display(emp, n);

Return 0;

}

Output:

Name     Age    Phone Number   Salary

Chirag   24     1234567788      20000

Arnav    31     1234567891      56000

Shivam   45     8881101111      30500

Q6) Define union?

A6) Union

Unions are quite similar to the structures in C. Union is also a derived type as structure. Union can be defined in same manner as structures just the keyword used in defining union in union where keyword used in defining structure was struct.

Union car

{

Char name[50];

Int price;

};

Union variables can be created in similar manner as structure variable.

Union car

{

Char name[50];

Int price;

}c1, c2, *c3;

OR;

Union car

{

Char name[50];

Int price;

};

-------Inside Function-----------

Union car c1, c2, *c3;

In both cases, union variables c1, c2 and union pointer variable c3 of type union car is created.

Q7) How do you access the members of the union?

A7) Access member of union

●       Array elements are accessed using the Subscript variable , Similarly Union members are accessed using dot [.] operator.

●       (.) is called as “union member Operator”.

●       Use this Operator in between “Union variable”&“member name”

Union employee

{

Int id;

Char name[50];

Float salary;

} ;

Void main()

{

Union employee e1= { 1, “ABC”, 50000 };

Printf(“%d”, e. Id);

Printf(“%s”, e. Name);

}

O/P-  garbage value, ABC

Q8) Compare structure and union?

A8) Structure Vs Union

Q9) Write a program to store information of students and display it?

A9) Program

#include <stdio.h>

#include <string.h>

Union Student

{

Int age;

Char Name[50];

Char Department[20];

};

Int main()

{

Union student stud1;

Union Employee stud2;

Stud1.age = 28;

Strcpy(stud1.Name, "Chris");

Strcpy(stud1.Department, "Science");

Printf("\nDetails of the First Student \n");

Printf("  Student Age = %d \n", emp1.age);

Printf("  Student Name = %s \n", emp1.Name);

Printf("  Student Department = %s \n", emp1.Department);

Printf("Details of the Second Student \n" );

Stud2.age = 30;

Printf("  Student Age = %d \n", stud2.age );

Strcpy(stud2.Name, "David");

Printf("  Student Name = %s \n", stud2.Name );

Strcpy(stud2.Department, "Technology" );

Printf("  Student Department = %s \n ", stud2.Department );

Return 0;

}

OUTPUT:

Details of the first student

Student Age = 28

Student Name = Chris

Student Department = Science

Details of the Second Student

Student Age =30

Student Name = David

Student Department= Technology

Q10) Write the advantages and disadvantages of structure?

A10) Advantages of structure

●       Structures gather more than one piece of data about the same subject together in the same place.

●       It is helpful when you want to gather the data of similar data types and parameters like first name, last name, etc.

●       It is very easy to maintain as we can represent the whole record by using a single name.

●       In structure, we can pass a complete set of records to any function using a single parameter.

●       You can use an array of structure to store more records with similar types.

Disadvantages of structure

●       If the complexity of an IT project goes beyond the limit, it becomes hard to manage.

●       Change of one data structure in a code necessitates changes at many other places. Therefore, the changes become hard to track.

●       Structure is slower because it requires storage space for all the data.

●       You can retrieve any member at a time in structure whereas you can access one member at a time in the union.

●       Structure occupies space for each and every member written in inner parameters while union occupies space for a member having the highest size written in inner parameters.

●       Structure supports a flexible array. Union does not support a flexible array.

Q11) Write an example for calloc ()?

A11) Program

Example of calloc()

#include<stdio.h>

#include<stdlib.h>

Int main()

{

Int n,i,*ptr,sum=0;

Printf("Enter number of elements: ");

Scanf("%d",&n);

Ptr=(int*)calloc(n,sizeof(int));  //memory allocated using calloc

If(ptr==NULL)

{

Printf("Sorry! unable to allocate memory");

Exit(0);

}

Printf("Enter elements of array: ");

For(i=0;i<n;++i)

{

Scanf("%d",ptr+i);

Sum+=*(ptr+i);

}

Printf("Sum=%d",sum);

Free(ptr);

Return 0;

}

Output

Enter elements of array: 3

Enter elements of array: 10

10

10

Sum=30

Q12) Explain nested structure?

A12) The feature of nesting one structure within another structure in C allows us to design complicated data types. For example, we could need to keep an entity employee's address in a structure. Street number, city, state, and pin code are all possible subparts of the attribute address. As a result, we must store the employee's address in a different structure and nest the structure address into the structure employee to store the employee's address.

In the following methods, the structure can be nested.

●      By separate structure

●      By Embedded structure

1) Separate structure

We've created two structures here, but the dependent structure should be utilised as a member inside the primary structure. Consider the following illustration.

Struct Date 

{ 

   int dd; 

   int mm; 

   int yyyy;  

}; 

Struct Employee 

{    

   int id; 

   char name[20]; 

   struct Date doj; 

}emp1; 

Doj (date of joining) is a Date variable, as you can see. In this case, doj is a member of the Employee structure. We may utilise the Date structure in a variety of structures this way.

2) Embedded structure

We can declare the structure inside the structure using the embedded structure. As a result, it uses fewer lines of code, but it cannot be applied to numerous data structures. Consider the following illustration.

Struct Employee 

{    

   int id; 

   char name[20]; 

   struct Date 

    { 

      int dd; 

      int mm; 

      int yyyy;  

    }doj; 

}emp1; 

Accessing Nested Structure

We can access the member of the nested structure by

Outer_Structure.Nested_Structure.member as given below:

e1.doj.dd 

e1.doj.mm

e1.doj.yyyy 

Example of Nested Structure

#include <stdio.h> 

#include <string.h> 

Struct Employee 

{    

   int id; 

   char name[20]; 

   struct Date 

    { 

      int dd; 

      int mm; 

      int yyyy;  

    }doj; 

}e1; 

Int main( ) 

{ 

   //storing employee information 

   e1.id=101; 

   strcpy(e1.name, "Sonoo Jaiswal");//copying string into char array 

   e1.doj.dd=10; 

   e1.doj.mm=11; 

   e1.doj.yyyy=2014; 

   //printing first employee information 

   printf( "employee id : %d\n", e1.id); 

   printf( "employee name : %s\n", e1.name); 

   printf( "employee date of joining (dd/mm/yyyy) : %d/%d/%d\n", e1.doj.dd,e1.doj.mm,e1.doj.yyyy); 

   return 0; 

}

Output:

Employee id : 101

Employee name : Sonoo Jaiswal

Employee date of joining (dd/mm/yyyy) : 10/11/2014

Q13) Write a program for nested strcuture?

A13) Consider the programme below.

#include<stdio.h> 

Struct address  

{ 

    char city[20]; 

    int pin; 

    char phone[14]; 

}; 

Struct employee 

{ 

    char name[20]; 

    struct address add; 

}; 

Void main () 

{ 

    struct employee emp; 

    printf("Enter employee information?\n"); 

    scanf("%s %s %d %s",emp.name,emp.add.city, &emp.add.pin, emp.add.phone); 

    printf("Printing the employee information....\n"); 

    printf("name: %s\nCity: %s\nPincode: %d\nPhone: %s",emp.name,emp.add.city,emp.add.pin,emp.add.phone); 

} 

Output

Enter employee information?

Arun           

Delhi          

110001      

1234567890   

Printing the employee information....  

Name: Arun     

City: Delhi 

Pincode: 110001

Phone: 1234567890

Q14) Describe an Array of structure with an example?

A14) In C, an array of structures is a collection of many structure variables, each of which contains information on a different entity. In C, an array of structures is used to store data about many entities of various data kinds. The collection of structures is another name for the array of structures.

Fig 1: Array of structure

Let's look at an array of structures that stores and outputs information for five students.

#include<stdio.h> 

#include <string.h>   

Struct student{   

Int rollno;   

Char name[10];   

};   

Int main(){   

Int i;   

Struct student st[5];   

Printf("Enter Records of 5 students");   

For(i=0;i<5;i++){   

Printf("\nEnter Rollno:");   

Scanf("%d",&st[i].rollno);   

Printf("\nEnter Name:");   

Scanf("%s",&st[i].name);   

}   

Printf("\nStudent Information List:");   

For(i=0;i<5;i++){   

Printf("\nRollno:%d, Name:%s",st[i].rollno,st[i].name);   

}   

   return 0;   

}  

Output:

Enter Records of 5 students

Enter Rollno:10

Enter Name:Sonu

Enter Rollno:20

Enter Name:Ratana

Enter Rollno:30

Enter Name:Vomika

Enter Rollno:40

Enter Name:James

Enter Rollno:50

Enter Name:Sadaf

Student Information List:

Rollno:10, Name:Sonu

Rollno:20, Name:Ratanaa

Rollno:30, Name:Vomika

Rollno:40, Name:James

Rollno:50, Name:Sadaf

Q15) Write a Program to access the structure member using the structure pointer and arrow (->) operator?

A15) Consider a C programme that uses the pointer and the arrow (->) operator to access structure members.

#include <stdio.h>

// create Employee structure  

Struct Employee 

{ 

    // define the member of the structure 

    char name[30]; 

    int id; 

    int age; 

    char gender[30]; 

    char city[40]; 

}; 

// define the variables of the Structure with pointers 

Struct Employee emp1, emp2, *ptr1, *ptr2; 

Int main() 

{ 

    // store the address of the emp1 and emp2 structure variable 

    ptr1 = &emp1; 

    ptr2 = &emp2; 

    printf (" Enter the name of the Employee (emp1): "); 

    scanf (" %s", &ptr1->name); 

    printf (" Enter the id of the Employee (emp1): "); 

    scanf (" %d", &ptr1->id); 

    printf (" Enter the age of the Employee (emp1): "); 

    scanf (" %d", &ptr1->age); 

    printf (" Enter the gender of the Employee (emp1): "); 

    scanf (" %s", &ptr1->gender); 

    printf (" Enter the city of the Employee (emp1): "); 

    scanf (" %s", &ptr1->city); 

    printf (" \n Second Employee: \n"); 

            printf (" Enter the name of the Employee (emp2): "); 

    scanf (" %s", &ptr2->name); 

    printf (" Enter the id of the Employee (emp2): "); 

    scanf (" %d", &ptr2->id); 

    printf (" Enter the age of the Employee (emp2): "); 

    scanf (" %d", &ptr2->age); 

    printf (" Enter the gender of the Employee (emp2): "); 

    scanf (" %s", &ptr2->gender); 

    printf (" Enter the city of the Employee (emp2): "); 

    scanf (" %s", &ptr2->city); 

    printf ("\n Display the Details of the Employee using Structure Pointer"); 

    printf ("\n Details of the Employee (emp1) \n"); 

    printf(" Name: %s\n", ptr1->name); 

    printf(" Id: %d\n", ptr1->id); 

    printf(" Age: %d\n", ptr1->age); 

    printf(" Gender: %s\n", ptr1->gender); 

    printf(" City: %s\n", ptr1->city); 

    printf ("\n Details of the Employee (emp2) \n"); 

    printf(" Name: %s\n", ptr2->name); 

    printf(" Id: %d\n", ptr2->id); 

    printf(" Age: %d\n", ptr2->age); 

    printf(" Gender: %s\n", ptr2->gender); 

    printf(" City: %s\n", ptr2->city); 

    return 0; 

}  

Output:

Enter the name of the Employee (emp1): John

Enter the id of the Employee (emp1): 1099

Enter the age of the Employee (emp1): 28

Enter the gender of the Employee (emp1): Male

Enter the city of the Employee (emp1): California

Second Employee: 

Enter the name of the Employee (emp2): Maria

Enter the id of the Employee (emp2): 1109

Enter the age of the Employee (emp2): 23

Enter the gender of the Employee (emp2): Female

Enter the city of the Employee (emp2): Los Angeles

Display the Details of the Employee using Structure Pointer

Details of the Employee (emp1)

Name: John

Id: 1099

Age: 28

Gender: Male

City: California

Details of the Employee (emp2) Name: Maria

Id: 1109

Age: 23

Gender: Female

City: Los Angeles

Q16) Write a Program to access the structure member using structure pointer and the dot operator?

A16) Consider the following example of creating a Subject structure and accessing its components with a structure pointer that points to the Subject variable's address in C.

#include <stdio.h> 

// create a structure Subject using the struct keyword 

Struct Subject 

{ 

    // declare the member of the Course structure 

    char sub_name[30]; 

    int sub_id; 

    char sub_duration[50]; 

    char sub_type[50]; 

}; 

Int main() 

{ 

    struct Subject sub; // declare the Subject variable 

    struct Subject *ptr; // create a pointer variable (*ptr)  

    ptr = ⊂ /* ptr variable pointing to the address of the structure variable sub */ 

    strcpy (sub.sub_name, " Computer Science"); 

    sub.sub_id = 1201; 

    strcpy (sub.sub_duration, "6 Months"); 

    strcpy (sub.sub_type, " Multiple Choice Question"); 

    // print the details of the Subject; 

    printf (" Subject Name: %s\t ", (*ptr).sub_name); 

            printf (" \n Subject Id: %d\t ", (*ptr).sub_id); 

        printf (" \n Duration of the Subject: %s\t ", (*ptr).sub_duration); 

           printf (" \n Type of the Subject: %s\t ", (*ptr).sub_type); 

    return 0; 

} 

Output:

Subject Name: Computer Science

Subject Id: 1201

Duration of the Subject: 6 Months

Type of the Subject: Multiple Choice Question

Q17) What is sizeof ()?

A17) In C, the sizeof() operator is frequently used. It determines the number of char-sized storage units used to store the expression or data type. The sizeof() operator has only one operand, which can either be an expression or a data typecast with the cast encapsulated in parenthesis. The data type can be pointer data types or complex data types like unions and structs, in addition to primitive data types like integer and floating data types.

Need of sizeof() operator

The storage size of basic data types is mostly known by programmes. The data type's storage size is constant, but it differs when implemented on different platforms. For example, we dynamically allocate the array space by using sizeof() operator:

Int *ptr=malloc(10*sizeof(int)); 

The sizeof() operation is applied to the cast of type int in the preceding example. The malloc() method is used to allocate memory and returns a reference to the memory that has been allocated. The memory space is calculated by multiplying the amount of bytes occupied by the int data type by ten.

Depending on the kind of operand, the sizeof() operator operates differently.

●      Operand is a data type

●      Operand is an expression

Q18) Define typedef?

A18) typedef

The typedef keyword is used in C programming to give meaningful names to variables that already exist in the programme. It works similarly to how we construct aliases for commands. In a nutshell, this keyword is used to change the name of a variable that already exists.

Syntax of typedef

Typedef <existing_name> <alias_name> 

'existing name' is the name of an already existing variable in the aforementioned syntax, while 'alias name' is another name for the same variable.

If we wish to create a variable of type unsigned int, for example, it will be a time-consuming operation if we want to declare several variables of this kind. We utilise the typedef keyword to solve the problem.

Typedef unsigned int unit; 

We used the typedef keyword to declare the unsigned int unit variable in the above statements.

By writing the following statement, we can now create variables of type unsigned int:

Unit a, b;  

Rather than writing:

Unsigned int a, b; 

So far, we've seen how the typedef keyword provides a convenient shortcut by offering an alternate name for a variable that already exists. This keyword comes in handy when working with lengthy data types, particularly structure declarations.

Example

#include <stdio.h> 

Int main() 

{ 

Typedef unsigned int unit; 

Unit i,j; 

i=10; 

j=20; 

Printf("Value of i is :%d",i); 

Printf("\nValue of j is :%d",j); 

Return 0; 

}

Output

Value of i is :10

Value of j is :20

Q19) Write notes on - fseek(), ftell() and rewind()?

A19) fseek()

To set the file pointer to a certain offset, use the fseek() function. It's used to save data to a file at a certain location.

Syntax:

Int fseek(FILE *stream, long int offset, int whence) 

Whence, the fseek() function uses three constants: SEEK SET, SEEK CUR, and SEEK END.

Example

#include <stdio.h> 

Void main(){ 

   FILE *fp; 

   fp = fopen("myfile.txt","w+"); 

   fputs("This is javatpoint", fp); 

   fseek( fp, 7, SEEK_SET ); 

   fputs("sonoo jaiswal", fp); 

   fclose(fp); 

} 

Output

This is sonam jaiswal

Ftell()

The ftell() function returns the supplied stream's current file position. After shifting the file pointer to the end of the file, we can use the ftell() function to retrieve the total size of the file. The SEEK END constant can be used to relocate the file pointer to the end of the file.

Syntax:

Long int ftell(FILE *stream) 

Example

#include <stdio.h> 

#include <conio.h> 

Void main (){ 

   FILE *fp; 

   int length; 

   clrscr(); 

   fp = fopen("file.txt", "r"); 

   fseek(fp, 0, SEEK_END); 

   length = ftell(fp); 

   fclose(fp); 

   printf("Size of file: %d bytes", length); 

   getch(); 

} 

Output:

Size of file: 21 bytes

Rewind()

The file pointer is set to the beginning of the stream using the rewind() function. It's useful if you'll be using stream frequently.

Syntax:

Void rewind(FILE *stream) 

Example

#include<stdio.h> 

#include<conio.h> 

Void main(){ 

FILE *fp; 

Char c; 

Clrscr(); 

Fp=fopen("file.txt","r"); 

While((c=fgetc(fp))!=EOF){ 

Printf("%c",c); 

} 

Rewind(fp);//moves the file pointer at beginning of the file 

While((c=fgetc(fp))!=EOF){ 

Printf("%c",c); 

} 

Fclose(fp);   

Getch();   

}   

Output:

This is a simple textthis is a simple text

The rewind() function, as you can see, moves the file pointer to the beginning of the file, which is why "this is simple text" is printed twice. If the rewind() function is not used, "this is simple text" will only be printed once.

Q20) What are the formatted input?

A20) scanf()

We utilize the scanf() function to get formatted or standard inputs so that the printf() function can give the programme a variety of conversion possibilities.

Syntax for scanf()

Scanf (format_specifier, &data_a, &data_b,……); // Here, & refers to the address operator

The scanf() function's goal is to read the characters from the standard input, convert them according to the format string, and then store the accessible inputs in the memory slots represented by the other arguments.

Example of scanf()

Scanf(“%d %c”, &info_a,&info_b);

The '&' character does not preface the data name when considering string data names in a programme.

Sscanf()

Int sscanf(const char *str, const char *format,...) is a C function that reads formatted input from a string.