UNIT 3 | unit 3 c programming

PPS

UNIT 3

C Programming

3.1 Problem specification

The process of problem-solving is an activity which has its ingredients as the specification of the program and the served dish is a correct program. This activity comprises of four steps:
1. Understanding the problem: To solve any problem it is very crucial to understand the problem first. What is the desired output of the code and how that output can be generated? The obvious and essential need to generate the output is an input. The input may be singular or it may be a set of inputs. A proper relationship between the input and output must be drawn in order to solve the problem efficiently. The input set should be complete and sufficient enough to draw the output. It means all the necessary inputs required to compute the output should be present at the time of computation. However, it should be kept in mind that the programmer should ensure that the minimum number of inputs should be there. Any irrelevant input only increases the size of and memory overhead of the program. Thus Identifying the minimum number of inputs required for output is a crucial element for understanding the problem.

2. Devising the plan: Once a problem has been understood, a proper action plan has to be devised to solve it. This is called devising the plan. This step usually involves computing the result from the given set of inputs. It uses the relationship drawn between inputs and outputs in the previous step. The complexity of this step depends upon the complexity of the problem at hand.

3. Executing the plan: Once the plan has been defined, it should follow the trajectory of action while ensuring the plan’s integrity at various checkpoints. If any inconsistency is found in between, the plan needs to be revised.

4. Evaluation: The final result so obtained must be evaluated and verified to see if the problem has been solved satisfactorily.

Problem Solving Methodology (The solution for the problem)

The methodology to solve a problem is defined as the most efficient solution to the problem. Although, there can be multiple ways to crack a nut, but a methodology is one where the nut is cracked in the shortest time and with minimum effort. Clearly, a sledgehammer can never be used to crack a nut. Under problem-solving methodology, we will see a step by step solution for a problem. These steps closely resemble the software life cycle. A software life cycle involves several stages in a program’s life cycle. These steps can be used by any tyro programmer to solve a problem in the most efficient way ever. The several steps of this cycle are as follows :

Step by step solution for a problem (Software Life Cycle)
1. Problem Definition/Specification: A computer program is basically a machine language solution to a real-life problem. Because programs are generally made to solve the pragmatic problems of the outside world. In order to solve the problem, it is very necessary to define the problem to get its proper understanding. For example, suppose we are asked to write a code for “ Compute the average of three numbers”. In this case, a proper definition of the problem will include questions like :
“What exactly does average mean?”
“How to calculate the average?”

Once, questions like these are raised, it helps to formulate the solution of the problem in a better way. Once a problem has been defined, the program’s specifications are then listed. Problem specifications describe what the program for the problem must do. It should definitely include :

INPUT :

What is the input set of the program

OUTPUT :

What is the desired output of the program and in what form the output is desired?

2. Problem Analysis (Breaking down the solution into simple steps): This step of solving the problem follows a modular approach to crack the nut. The problem is divided into sub problems so that designing a solution to these subproblems gets easier. The solutions to all these individual parts are then merged to get the final solution of the original problem. It is like divide and merge approach.

Modular Approach for Programming :

The process of breaking a large problem into sub problems and then treating these individual parts as different functions is called modular programming. Each function behaves independent of another and there is minimal inter-functional communication. There are two methods to implement modular programming :

Top Down Design : In this method, the original problem is divided into subparts. These subparts are further divided. The chain continues till we get the very fundamental subpart of the problem which can’t be further divided. Then we draw a solution for each of these fundamental parts.
Bottom Up Design : In this style of programming, an application is written by using the pre-existing primitives of programming language. These primitives are then amalgamated with more complicated features, till the application is written. This style is just the reverse of the top-down design style.

3. Problem Designing: The design of a problem can be represented in either of the two forms :

Algorithm: The set of instructions written down to formulate the solution of a problem is called algorithm. These instructions when followed to write the code produces the desired output. The steps involved in the algorithm are usually written in English or any colloquial language which is easier for the programmer to comprehend what the code needs.
Let’s have a mundane example preparing the early morning tea and write an algorithm for the same.
STEP 1: START
STEP 2: Pour water in a pan.
STEP 3: Put the pan on gas burner.
STEP 4: Light the gas burner.
STEP 5: Put sugar in the pan.
STEP 6: Put tea leaves in the pan.
STEP 7: Pour milk in the pan.
STEP 8: Filter the prepared tea in the cup.
STEP 9: Serve it to others and enjoy yourself.
STEp 10 : STOP

The ways to execute any program are of three categories:

Sequence Statements
Here, all the instructions are executed in a sequence, that is, one after the another, till the program is executed.
Selection Statements
As it is self-clear from the name, in these type of statements the whole set of instructions is not executed. A selection has to be made. A selected number of instructions are executed based on some condition. If the condition holds true then some part of the instruction set is executed, otherwise, another part of the set is executed. Since this selection out of the instruction set has to be made, thus these type of instructions are called Selection Statements.
Iteration or Looping Statements
As lucid by the name itself, here a particular set of instructions is being executed multiple times. This set of instructions keeps on executing in a loop until a particular condition gets terminated. These types of instructions are also called iteration statements.

The three ways of executing a program explained above are also termed as ‘control structure’ since they determine and control the flow of execution in a set of statements.

Identification of arithmetic and logical operations required for the solution:
While writing the algorithm for a problem, the arithmetic and logical operations required for the solution are also usually identified. They help to write the code in an easier manner because the proper ordering of the arithmetic and logical symbols is necessary to determine the correct output. And when all this has been done in the algorithm writing step, it just makes the coding task a smoother one.

2. Flow Chart: Flow charts are diagrammatic representation of the algorithm. It uses some symbols to illustrate the starting and ending of a program along with the flow of instructions involved in the program.

4. Coding: Once an algorithm is formed, it can’t be executed on the computer. Thus in this step, this algorithm has to be translated into the syntax of a particular programming language. This process is often termed as ‘coding’. Coding is one of the most important steps of the software life cycle. It is not only challenging to find a solution to a problem but to write optimized code for a solution is far more challenging.

Writing code for optimizing execution time and memory storage :
A programmer writes code on his local computer. Now, suppose he writes a code which takes 5 hours to get executed. Now, this 5 hours of time is actually the idle time for the programmer. Not only it takes longer time, but it also uses the resources during that time. One of the most precious computing resources is memory. A large program is expected to utilize more memory. However, memory utilization is not a fault, but if a program is utilizing unnecessary time or memory, then it is a fault of coding. The optimized code can save both time and memory. For example, as has been discussed earlier, by using the minimum number of inputs to compute the output, one can save unnecessary memory utilization. All such techniques are very necessary to be deployed to write optimized code. The pragmatic world gives reverence not only to the solution of the problem but to the optimized solution. This art of writing the optimized code also called ‘competitive programming’.

5. Program Testing and Debugging: Program testing involves running each and every instruction of the code and check the validity of the output by a sample input. By testing a program one can also check if there’s an error in the program. If an error is detected, then program debugging is done. It is a process to locate the instruction which is causing an error in the program and then rectifying it. There are different types of error in a program :
(i) Syntax Error
Every programming language has its own set of rules and constructs which need to be followed to form a valid program in that particular language. If at any place in the entire code, this set of rule is violated, it results in a syntax error.
Take an example in C Language

#include <stdio.h>

Voidmain()

{

Charans[50];

Printf("how are you?")

Gets(ans);

Printf("\ngood to see that you are %s", ans);

}

In the above program, the syntax error is in the first printf statement since the printf statement doesn’t end with a ‘;’. Now, until and unless this error is not rectified, the program will not get executed.

Once the error is rectified, one gets the desired output. Suppose the input is ‘good’ then the output is :
Output:

How are you

Good to see that you are good

(ii) Logical Error
An error caused due to the implementation of a wrong logic in the program is called logical error. They are usually detected during the runtime.
Take an example in C Language:

#include <stdio.h>

Voidmain()

{

Intn = 11, i;

For(i = n; i <= 10; i++)

Printf("%d\n", i);

}

In the above code, the ‘for’ loop won’t get executed since n has been initialized with the value of 11 while ‘for’ loop can only print values smaller than or equal to 10. Such a code will result in incorrect output and thus errors like these are called logical errors.
Once the error is rectified, one gets the desired output. Suppose n is initialised with the value ‘5’ then the output is :
Output:

(iii) Runtime Error
Any error which causes the unusual termination of the program is called runtime error. They are detected at the run time.
Some common examples of runtime errors are :
Example 1 :

#include <stdio.h>

Voidmain()

{

Inta, b, c;

Printf("enter the value of a and b");

Scanf("%d%d", &a, &b);

c = a / b;

Printf("The quotient when a is divided by b is %d\n", c);

}

If during the runtime, the user gives the input value for B as 0 then the program terminates abruptly resulting in a runtime error. The output thus appears is :
Output:

NO OUTPUT

Floating Point Exception

Example 2 :
If while executing a program, one attempts for opening an unexisting file, that is, a file which is not present in the hard disk, it also results in a runtime error.

6. Documentation: The program documentation involves :

Problem Definition
Problem Design
Documentation of test perform
History of program development
User’s manual

A user’s manual is used by a user to know about a program’s input, processing, and output data.

7. Program Maintenance : Once a program has been formed, to ensure its longevity, maintenance is a must. The maintenance of a program has its own costs associated with it, which may also exceed the development cost of the program in some cases. The maintenance of a program involves the following :

Detection and Elimination of undetected errors in the existing program.
Modification of current program to enhance its performance and
adaptability.
Enhancement of user interface
Enriching the program with new capabilities.
Updation of the documentation.

Control Structure- Conditional control and looping (finite and infinite)

There are codes which usually involve looping statements. Looping statements are statements in which instruction or a set of instructions is executed multiple times until a particular condition is satisfied. The while loop, for loop, do while loop, etc. form the basis of such looping structure. These statements are also called control structure because they determine or control the flow of instructions in a program. These looping structures are of two kinds :

Conditional Control ( Finite Looping )
In this looping, the loop gets executed a finite number of times. Once a particular condition is satisfied, the loop gets terminated.
Take an example in C language :

#include <stdio.h>

Voidmain()

{

Intn = 1, i;

For(i = n; i <= 10; i++)

Printf("%d\n", i);

}

In the above program, the ‘for’ loop gets executed only until the value of i is less than or equal to 10. As soon as the value of i becomes greater than 10, the while loop is terminated.
Output:

10 //loop gets terminated

2. Infinite Looping
The infinite looping control structure is just the opposite of finite looping control structure. Here, the condition to terminate the loop never gets satisfied and hence, the loop gets executed infinitely.
Take an example in Python language :

#include <stdio.h>

Voidmain()

{

Intn = 1;

While(n <= 10)

Printf("%d\n", n);

}

In the above code, one can easily see that the value of n is not getting incremented. In such a case, the value of n will always remain 1 and hence the while loop will never get executed. Such loop is called an infinite loop.
Output:

.. //loop never terminates

3.2 Flow chart

Flowchart is a diagrammatic representation of sequence of logical steps of a program. Flowcharts use simple geometric shapes to depict processes and arrows to show relationships and process/data flow.

Flowchart Symbols

Here is a chart for some of the common symbols used in drawing flowcharts.

Symbol	Symbol Name	Purpose
	Start/Stop	Used at the beginning and end of the algorithm to show start and end of the program.
	Process	Indicates processes like mathematical operations.
	Input/ Output	Used for denoting program inputs and outputs.
	Decision	Stands for decision statements in a program, where answer is usually Yes or No.
	Arrow	Shows relationships between different shapes.
	On-page Connector	Connects two or more parts of a flowchart, which are on the same page.
	Off-page Connector	Connects two parts of a flowchart which are spread over different pages.

Guidelines for Developing Flowcharts

These are some points to keep in mind while developing a flowchart −

Flowchart can have only one start and one stop symbol
On-page connectors are referenced using numbers
Off-page connectors are referenced using alphabets
General flow of processes is top to bottom or left to right
Arrows should not cross each other

Example Flowcharts

Here is the flowchart for going to the market to purchase a pen.

Here is a flowchart to calculate the average of two numbers.

3.3 Data types

A data type specifies the type of data that a variable can store such as integer, floating, character, etc.

There are the following data types in C language.

Types	Data Types
Basic Data Type	Int, char, float, double
Derived Data Type	Array, pointer, structure, union
Enumeration Data Type	Enum
Void Data Type	Void

Basic Data Types

The basic data types are integer-based and floating-point based. C language supports both signed and unsigned literals.

The memory size of the basic data types may change according to 32 or 64-bit operating system.

Let's see the basic data types. Its size is given according to 32-bit architecture.

Data Types	Memory Size	Range
Char	1 byte	−128 to 127
Signed char	1 byte	−128 to 127
Unsigned char	1 byte	0 to 255
Short	2 byte	−32,768 to 32,767
Signed short	2 byte	−32,768 to 32,767
Unsigned short	2 byte	0 to 65,535
Int	2 byte	−32,768 to 32,767
Signed int	2 byte	−32,768 to 32,767
Unsigned int	2 byte	0 to 65,535
Short int	2 byte	−32,768 to 32,767
Signed short int	2 byte	−32,768 to 32,767
Unsigned short int	2 byte	0 to 65,535
Long int	4 byte	-2,147,483,648 to 2,147,483,647
Signed long int	4 byte	-2,147,483,648 to 2,147,483,647
Unsigned long int	4 byte	0 to 4,294,967,295
Float	4 byte
Double	8 byte
Long double	10 byte

3.4 Assignment statements

The following table lists the assignment operators supported by the C language −

Operator	Description	Example
=	Simple assignment operator. Assigns values from right side operands to left side operand	C = A + B will assign the value of A + B to C
+=	Add AND assignment operator. It adds the right operand to the left operand and assign the result to the left operand.	C += A is equivalent to C = C + A
-=	Subtract AND assignment operator. It subtracts the right operand from the left operand and assigns the result to the left operand.	C -= A is equivalent to C = C - A
*=	Multiply AND assignment operator. It multiplies the right operand with the left operand and assigns the result to the left operand.	C = A is equivalent to C = C A
/=	Divide AND assignment operator. It divides the left operand with the right operand and assigns the result to the left operand.	C /= A is equivalent to C = C / A
%=	Modulus AND assignment operator. It takes modulus using two operands and assigns the result to the left operand.	C %= A is equivalent to C = C % A
<<=	Left shift AND assignment operator.	C <<= 2 is same as C = C << 2
>>=	Right shift AND assignment operator.	C >>= 2 is same as C = C >> 2
&=	Bitwise AND assignment operator.	C &= 2 is same as C = C & 2
^=	Bitwise exclusive OR and assignment operator.	C ^= 2 is same as C = C ^ 2
\|=	Bitwise inclusive OR and assignment operator.	C \|= 2 is same as C = C \| 2

Example

Try the following example to understand all the assignment operators available in C −

#include<stdio.h>

Main(){

Int a =21;

Int c ;

c = a;

Printf("Line 1 - = Operator Example, Value of c = %d\n", c );

c += a;

Printf("Line 2 - += Operator Example, Value of c = %d\n", c );

c -= a;

Printf("Line 3 - -= Operator Example, Value of c = %d\n", c );

c*= a;

Printf("Line 4 - *= Operator Example, Value of c = %d\n", c );

c/= a;

Printf("Line 5 - /= Operator Example, Value of c = %d\n", c );

c =200;

c%= a;

Printf("Line 6 - %= Operator Example, Value of c = %d\n", c );

c <<=2;

Printf("Line 7 - <<= Operator Example, Value of c = %d\n", c );

c >>=2;

Printf("Line 8 - >>= Operator Example, Value of c = %d\n", c );

c&=2;

Printf("Line 9 - &= Operator Example, Value of c = %d\n", c );

c^=2;

Printf("Line 10 - ^= Operator Example, Value of c = %d\n", c );

c|=2;

Printf("Line 11 - |= Operator Example, Value of c = %d\n", c );

}

When you compile and execute the above program, it produces the following result −

Line 1 - = Operator Example, Value of c = 21

Line 2 - += Operator Example, Value of c = 42

Line 3 - -= Operator Example, Value of c = 21

Line 4 - *= Operator Example, Value of c = 441

Line 5 - /= Operator Example, Value of c = 21

Line 6 - %= Operator Example, Value of c = 11

Line 7 - <<= Operator Example, Value of c = 44

Line 8 - >>= Operator Example, Value of c = 11

Line 9 - &= Operator Example, Value of c = 2

Line 10 - ^= Operator Example, Value of c = 0

Line 11 - |= Operator Example, Value of c = 2

3.5 Input Output statements

There are some library functions which are available for transferring the information between the computer and the standard input and output devices.
These functions are related to the symbolic constants and are available in the header file.

Some of the input and output functions are as follows:

i) printf
This function is used for displaying the output on the screen i.e the data is moved from the computer memory to the output device.

Syntax:
printf(“format string”, arg1, arg2, …..);

In the above syntax, 'format string' will contain the information that is formatted. They are the general characters which will be displayed as they are .
arg1, arg2 are the output data items.

Example: Demonstrating the printf function
printf(“Enter a value:”);

Printf will generally examine from left to right of the string.
The characters are displayed on the screen in the manner they are encountered until it comes across % or \.
Once it comes across the conversion specifiers it will take the first argument and print it in the format given.

Ii) scanf
scanf is used when we enter data by using an input device.

Syntax:
scanf (“format string”, &arg1, &arg2, …..);

The number of items which are successful are returned.

Format string consists of the conversion specifier. Arguments can be variables or array name and represent the address of the variable. Each variable must be preceded by an ampersand (&). Array names should never begin with an ampersand.

Example: Demonstrating scanf
int avg;
float per;
char grade;
scanf(“%d %f %c”,&avg, &per, &grade):

Scanf works totally opposite to printf. The input is read, interpret using the conversion specifier and stores it in the given variable.
The conversion specifier for scanf is the same as printf.
Scanf reads the characters from the input as long as the characters match or it will terminate. The order of the characters that are entered are not important.
It requires an enter key in order to accept an input.

Iii) getch
This function is used to input a single character. The character is read instantly and it does not require an enter key to be pressed. The character type is returned but it does not echo on the screen.

Syntax:
int getch(void);
ch=getch();

where,
ch - assigned the character that is returned by getch.

iv) putch
this function is a counterpart of getch. Which means that it will display a single character on the screen. The character that is displayed is returned.

Syntax:
int putch(int);
putch(ch);

where,
ch - the character that is to be printed.

v) getche
This function is used to input a single character. The main difference between getch and getche is that getche displays the (echoes) the character that we type on the screen.

Syntax:
int getch(void);
ch=getche();

vi) getchar
This function is used to input a single character. The enter key is pressed which is followed by the character that is typed. The character that is entered is echoed.

Syntax:
ch=getchar;

vii) putchar
This function is the other side of getchar. A single character is displayed on the screen.

Syntax:
putchar(ch);

viii) gets and puts
They help in transferring the strings between the computer and the standard input-output devices. Only single arguments are accepted. The arguments must be such that it represents a string. It may include white space characters. If gets is used enter key has to be pressed for ending the string. The gets and puts function are used to offer simple alternatives of scanf and printf for reading and displaying.

Example:

#include <stdio.h>
void main()
{
    char line[30];
    gets (line);
    puts (line);
}

3.6 Developing simple C programs

To write the first c program, open the C console and write the following code:

#include <stdio.h>
Int main(){
Printf("Hello C Language");
Return 0;
}

#include <stdio.h> includes the standard input output library functions. The printf() function is defined in stdio.h .

Int main() The main() function is the entry point of every program in c language.

Printf() The printf() function is used to print data on the console.

Return 0 The return 0 statement, returns execution status to the OS. The 0 value is used for successful execution and 1 for unsuccessful execution.

How to compile and run the c program

There are 2 ways to compile and run the c program, by menu and by shortcut.

By menu

Now click on the compile menu then compile sub menu to compile the c program.

Then click on the run menu then run sub menu to run the c program.

By shortcut

Or, press ctrl+f9 keys compile and run the program directly.

You will see the following output on user screen.

You can view the user screen any time by pressing the alt+f5 keys.

Now press Esc to return to the turbo c++ console.

3.7 If statement, for loops, while loops, do-while loops, switch statement, break statement, continue statement, development of C programs using above statements

C if else Statement

The if-else statement in C is used to perform the operations based on some specific condition. The operations specified in if block are executed if and only if the given condition is true.

There are the following variants of if statement in C language.

If statement
If-else statement
If else-if ladder
Nested if

If Statement

The if statement is used to check some given condition and perform some operations depending upon the correctness of that condition. It is mostly used in the scenario where we need to perform the different operations for the different conditions. The syntax of the if statement is given below.

If(expression){
//code to be executed
}

Flowchart of if statement in C

Let's see a simple example of C language if statement.

#include<stdio.h>
Int main(){
Int number=0;
Printf("Enter a number:");
Scanf("%d",&number);
If(number%2==0){
Printf("%d is even number",number);
}
Return 0;
}

Output

Enter a number:4

4 is even number

Enter a number:5

Program to find the largest number of the three.

#include <stdio.h>
Int main()
{
Int a, b, c;
Printf("Enter three numbers?");
Scanf("%d %d %d",&a,&b,&c);
If(a>b && a>c)
{
Printf("%d is largest",a);
}
If(b>a && b > c)
{
Printf("%d is largest",b);
}
If(c>a && c>b)
{
Printf("%d is largest",c);
}
If(a == b && a == c)
{
Printf("All are equal");
}
}

Output

Enter three numbers?

12 23 34

34 is largest

If-else Statement

The if-else statement is used to perform two operations for a single condition. The if-else statement is an extension to the if statement using which, we can perform two different operations, i.e., one is for the correctness of that condition, and the other is for the incorrectness of the condition. Here, we must notice that if and else block cannot be executed simiulteneously. Using if-else statement is always preferable since it always invokes an otherwise case with every if condition. The syntax of the if-else statement is given below.

If(expression){
//code to be executed if condition is true
}else{
//code to be executed if condition is false
}

Flowchart of the if-else statement in C

Let's see the simple example to check whether a number is even or odd using if-else statement in C language.

#include<stdio.h>
Int main(){
Int number=0;
Printf("enter a number:");
Scanf("%d",&number);
If(number%2==0){
Printf("%d is even number",number);
}
Else{
Printf("%d is odd number",number);
}
Return 0;
}

Output

Enter a number:4

4 is even number

Enter a number:5

5 is odd number

Program to check whether a person is eligible to vote or not.

#include <stdio.h>
Int main()
{
Int age;
Printf("Enter your age?");
Scanf("%d",&age);
If(age>=18)
{
Printf("You are eligible to vote...");
}
Else
{
Printf("Sorry ... you can't vote");
}
}

Output

Enter your age?18

You are eligible to vote...

Enter your age?13

Sorry ... You can't vote

If else-if ladder Statement

The if-else-if ladder statement is an extension to the if-else statement. It is used in the scenario where there are multiple cases to be performed for different conditions. In if-else-if ladder statement, if a condition is true then the statements defined in the if block will be executed, otherwise if some other condition is true then the statements defined in the else-if block will be executed, at the last if none of the condition is true then the statements defined in the else block will be executed. There are multiple else-if blocks possible. It is similar to the switch case statement where the default is executed instead of else block if none of the cases is matched.

If(condition1){
//code to be executed if condition1 is true
}else if(condition2){
//code to be executed if condition2 is true
}
Else if(condition3){
//code to be executed if condition3 is true
}
...
Else{
//code to be executed if all the conditions are false
}

Flowchart of else-if ladder statement in C

The example of an if-else-if statement in C language is given below.

#include<stdio.h>
Int main(){
Int number=0;
Printf("enter a number:");
Scanf("%d",&number);
If(number==10){
Printf("number is equals to 10");
}
Else if(number==50){
Printf("number is equal to 50");
}
Else if(number==100){
Printf("number is equal to 100");
}
Else{
Printf("number is not equal to 10, 50 or 100");
}
Return 0;
}

Output

Enter a number:4

Number is not equal to 10, 50 or 100

Enter a number:50

Number is equal to 50

Program to calculate the grade of the student according to the specified marks.

#include <stdio.h>
Int main()
{
Int marks;
Printf("Enter your marks?");
Scanf("%d",&marks);
If(marks > 85 && marks <= 100)
{
Printf("Congrats ! you scored grade A ...");
}
Else if (marks > 60 && marks <= 85)
{
Printf("You scored grade B + ...");
}
Else if (marks > 40 && marks <= 60)
{
Printf("You scored grade B ...");
}
Else if (marks > 30 && marks <= 40)
{
Printf("You scored grade C ...");
}
Else
{
Printf("Sorry you are fail ...");
}
}

Output

Enter your marks?10

Sorry you are fail ...

Enter your marks?40

You scored grade C ...

Enter your marks?90

Congrats !you scored grade A ...

C Switch Statement

The switch statement in C is an alternate to if-else-if ladder statement which allows us to execute multiple operations for the different possibles values of a single variable called switch variable. Here, We can define various statements in the multiple cases for the different values of a single variable.

The syntax of switch statement in c language is given below:

Switch(expression){
Case value1:
//code to be executed;
Break; //optional
Case value2:
//code to be executed;
Break; //optional
......
Default:
Code to be executed if all cases are not matched;
}

Rules for switch statement in C language

1) The switch expression must be of an integer or character type.

2) The case value must be an integer or character constant.

3) The case value can be used only inside the switch statement.

4) The break statement in switch case is not must. It is optional. If there is no break statement found in the case, all the cases will be executed present after the matched case. It is known as fall through the state of C switch statement.

Let's try to understand it by the examples. We are assuming that there are following variables.

Int x,y,z;
Char a,b;
Float f;

Valid Switch	Invalid Switch	Valid Case	Invalid Case
Switch(x)	Switch(f)	Case 3;	Case 2.5;
Switch(x>y)	Switch(x+2.5)	Case 'a';	Case x;
Switch(a+b-2)		Case 1+2;	Case x+2;
Switch(func(x,y))		Case 'x'>'y';	Case 1,2,3;

Flowchart of switch statement in C

Functioning of switch case statement

First, the integer expression specified in the switch statement is evaluated. This value is then matched one by one with the constant values given in the different cases. If a match is found, then all the statements specified in that case are executed along with the all the cases present after that case including the default statement. No two cases can have similar values. If the matched case contains a break statement, then all the cases present after that will be skipped, and the control comes out of the switch. Otherwise, all the cases following the matched case will be executed.

Let's see a simple example of c language switch statement.

#include<stdio.h>
Int main(){
Int number=0;
Printf("enter a number:");
Scanf("%d",&number);
Switch(number){
Case 10:
Printf("number is equals to 10");
Break;
Case 50:
Printf("number is equal to 50");
Break;
Case 100:
Printf("number is equal to 100");
Break;
Default:
Printf("number is not equal to 10, 50 or 100");
}
Return 0;
}

Output

Enter a number:4

Number is not equal to 10, 50 or 100

Enter a number:50

Number is equal to 50

Switch case example 2

#include <stdio.h>
Int main()
{
Int x = 10, y = 5;
Switch(x>y && x+y>0)
{
Case 1:
Printf("hi");
Break;
Case 0:
Printf("bye");
Break;
Default:
Printf(" Hello bye ");
}
}

Output

C Switch statement is fall-through

In C language, the switch statement is fall through; it means if you don't use a break statement in the switch case, all the cases after the matching case will be executed.

Let's try to understand the fall through state of switch statement by the example given below.

#include<stdio.h>
Int main(){
Int number=0;
Printf("enter a number:");
Scanf("%d",&number);
Switch(number){
Case 10:
Printf("number is equal to 10\n");
Case 50:
Printf("number is equal to 50\n");
Case 100:
Printf("number is equal to 100\n");
Default:
Printf("number is not equal to 10, 50 or 100");
}
Return 0;
}

Output

Enter a number:10

Number is equal to 10

Number is equal to 50

Number is equal to 100

Number is not equal to 10, 50 or 100

Output

Enter a number:50

Number is equal to 50

Number is equal to 100

Number is not equal to 10, 50 or 100

Nested switch case statement

We can use as many switch statement as we want inside a switch statement. Such type of statements is called nested switch case statements. Consider the following example.

#include <stdio.h>
Int main () {
Int i = 10;
Int j = 20;
Switch(i) {
Case 10:
Printf("the value of i evaluated in outer switch: %d\n",i);
Case 20:
Switch(j) {
Case 20:
Printf("The value of j evaluated in nested switch: %d\n",j);
}
}
Printf("Exact value of i is : %d\n", i );
Printf("Exact value of j is : %d\n", j );
Return 0;
}

Output

The value of i evaluated in outer switch: 10

The value of j evaluated in nested switch: 20

Exact value of i is : 10

Exact value of j is : 20

If-else vs switch

What is an if-else statement?

An if-else statement in C programming is a conditional statement that executes a different set of statements based on the condition that is true or false. The 'if' block will be executed only when the specified condition is true, and if the specified condition is false, then the else block will be executed.

Syntax of if-else statement is given below:

If(expression)
{
// statements;
}
Else
{
// statements;
}

What is a switch statement?

A switch statement is a conditional statement used in C programming to check the value of a variable and compare it with all the cases. If the value is matched with any case, then its corresponding statements will be executed. Each case has some name or number known as the identifier. The value entered by the user will be compared with all the cases until the case is found. If the value entered by the user is not matched with any case, then the default statement will be executed.

Syntax of the switch statement is given below:

Switch(expression)
{
Case constant 1:
// statements;
Break;
Case constant 2:
// statements;
Break;
Case constant n:
// statements;
Break;
Default:
// statements;
}

Similarity b/w if-else and switch

Both the if-else and switch are the decision-making statements. Here, decision-making statements mean that the output of the expression will decide which statements are to be executed.

Differences b/w if-else and switch statement

The following are the differences between if-else and switch statement are:

Definition

If-else

Based on the result of the expression in the 'if-else' statement, the block of statements will be executed. If the condition is true, then the 'if' block will be executed otherwise 'else' block will execute.

Switch statement

The switch statement contains multiple cases or choices. The user will decide the case, which is to execute.

Expression

If-else

It can contain a single expression or multiple expressions for multiple choices. In this, an expression is evaluated based on the range of values or conditions. It checks both equality and logical expressions.

Switch

It contains only a single expression, and this expression is either a single integer object or a string object. It checks only equality expression.

Evaluation

If-else

An if-else statement can evaluate almost all the types of data such as integer, floating-point, character, pointer, or Boolean.

Switch

A switch statement can evaluate either an integer or a character.

Sequence of Execution

If-else

In the case of 'if-else' statement, either the 'if' block or the 'else' block will be executed based on the condition.

Switch

In the case of the 'switch' statement, one case after another will be executed until the break keyword is not found, or the default statement is executed.

Default Execution

If-else

If the condition is not true within the 'if' statement, then by default, the else block statements will be executed.

Switch

If the expression specified within the switch statement is not matched with any of the cases, then the default statement, if defined, will be executed.

Values

If-else

Values are based on the condition specified inside the 'if' statement. The value will decide either the 'if' or 'else' block is to be executed.

Switch

In this case, value is decided by the user. Based on the choice of the user, the case will be executed.

If-else

It evaluates a condition to be true or false.

Switch

A switch statement compares the value of the variable with multiple cases. If the value is matched with any of the cases, then the block of statements associated with this case will be executed.

Editing

If-else

Editing in 'if-else' statement is not easy as if we remove the 'else' statement, then it will create the havoc.

Switch

Editing in switch statement is easier as compared to the 'if-else' statement. If we remove any of the cases from the switch, then it will not interrupt the execution of other cases. Therefore, we can say that the switch statement is easy to modify and maintain.

Speed

If-else

If the choices are multiple, then the speed of the execution of 'if-else' statements is slow.

Switch

The case constants in the switch statement create a jump table at the compile time. This jump table chooses the path of the execution based on the value of the expression. If we have a multiple choice, then the execution of the switch statement will be much faster than the equivalent logic of 'if-else' statement.

Let's summarize the above differences in a tabular form.

	If-else	Switch
Definition	Depending on the condition in the 'if' statement, 'if' and 'else' blocks are executed.	The user will decide which statement is to be executed.
Expression	It contains either logical or equality expression.	It contains a single expression which can be either a character or integer variable.
Evaluation	It evaluates all types of data, such as integer, floating-point, character or Boolean.	It evaluates either an integer, or character.
Sequence of execution	First, the condition is checked. If the condition is true then 'if' block is executed otherwise 'else' block	It executes one case after another till the break keyword is not found, or the default statement is executed.
Default execution	If the condition is not true, then by default, else block will be executed.	If the value does not match with any case, then by default, default statement is executed.
Editing	Editing is not easy in the 'if-else' statement.	Cases in a switch statement are easy to maintain and modify. Therefore, we can say that the removal or editing of any case will not interrupt the execution of other cases.
Speed	If there are multiple choices implemented through 'if-else', then the speed of the execution will be slow.	If we have multiple choices then the switch statement is the best option as the speed of the execution will be much higher than 'if-else'.

C Loops

The looping can be defined as repeating the same process multiple times until a specific condition satisfies. There are three types of loops used in the C language. In this part of the tutorial, we are going to learn all the aspects of C loops.

Why use loops in C language?

The looping simplifies the complex problems into the easy ones. It enables us to alter the flow of the program so that instead of writing the same code again and again, we can repeat the same code for a finite number of times. For example, if we need to print the first 10 natural numbers then, instead of using the printf statement 10 times, we can print inside a loop which runs up to 10 iterations.

Advantage of loops in C

1) It provides code reusability.

2) Using loops, we do not need to write the same code again and again.

3) Using loops, we can traverse over the elements of data structures (array or linked lists).

Types of C Loops

There are three types of loops in C language that is given below:

Do while
While
For

Do-while loop in C

The do-while loop continues until a given condition satisfies. It is also called post tested loop. It is used when it is necessary to execute the loop at least once (mostly menu driven programs).

The syntax of do-while loop in c language is given below:

Do{
//code to be executed
}while(condition);

While loop in C

The while loop in c is to be used in the scenario where we don't know the number of iterations in advance. The block of statements is executed in the while loop until the condition specified in the while loop is satisfied. It is also called a pre-tested loop.

The syntax of while loop in c language is given below:

While(condition){
//code to be executed
}

For loop in C

The for loop is used in the case where we need to execute some part of the code until the given condition is satisfied. The for loop is also called as a per-tested loop. It is better to use for loop if the number of iteration is known in advance.

The syntax of for loop in c language is given below:

For(initialization;condition;incr/decr){
//code to be executed
}

Do while loop in C

The do while loop is a post tested loop. Using the do-while loop, we can repeat the execution of several parts of the statements. The do-while loop is mainly used in the case where we need to execute the loop at least once. The do-while loop is mostly used in menu-driven programs where the termination condition depends upon the end user.

do while loop syntax

The syntax of the C language do-while loop is given below:

Do{
//code to be executed
}while(condition);

Example 1

#include<stdio.h>
#include<stdlib.h>
Void main ()
{
Char c;
Int choice,dummy;
Do{
Printf("\n1. Print Hello\n2. Print Javatpoint\n3. Exit\n");
Scanf("%d",&choice);
Switch(choice)
{
Case 1 :
Printf("Hello");
Break;
Case 2:
Printf("Javatpoint");
Break;
Case 3:
Exit(0);
Break;
Default:
Printf("please enter valid choice");
}
Printf("do you want to enter more?");
Scanf("%d",&dummy);
Scanf("%c",&c);
}while(c=='y');
}

Output

1. Print Hello

2. Print Javatpoint

3. Exit

Hello

Do you want to enter more?

1. Print Hello

2. Print Javatpoint

3. Exit

Javatpoint

Do you want to enter more?

Flowchart of do while loop

do while example

There is given the simple program of c language do while loop where we are printing the table of 1.

#include<stdio.h>
Int main(){
Int i=1;
Do{
Printf("%d \n",i);
i++;
}while(i<=10);
Return 0;
}

Output

Program to print table for the given number using do while loop

#include<stdio.h>
Int main(){
Int i=1,number=0;
Printf("Enter a number: ");
Scanf("%d",&number);
Do{
Printf("%d \n",(number*i));
i++;
}while(i<=10);
Return 0;
}

Output

Enter a number: 5

Enter a number: 10

100

Infinitive do while loop

The do-while loop will run infinite times if we pass any non-zero value as the conditional expression.

Do{
//statement
}while(1);

While loop in C

While loop is also known as a pre-tested loop. In general, a while loop allows a part of the code to be executed multiple times depending upon a given boolean condition. It can be viewed as a repeating if statement. The while loop is mostly used in the case where the number of iterations is not known in advance.

Syntax of while loop in C language

The syntax of while loop in c language is given below:

While(condition){
//code to be executed
}

Flowchart of while loop in C

Example of the while loop in C language

Let's see the simple program of while loop that prints table of 1.

#include<stdio.h>
Int main(){
Int i=1;
While(i<=10){
Printf("%d \n",i);
i++;
}
Return 0;
}

Output

Program to print table for the given number using while loop in C

#include<stdio.h>
Int main(){
Int i=1,number=0,b=9;
Printf("Enter a number: ");
Scanf("%d",&number);
While(i<=10){
Printf("%d \n",(number*i));
i++;
}
Return 0;
}

Output

Enter a number: 50

100

150

200

250

300

350

400

450

500

Enter a number: 100

100

200

300

400

500

600

700

800

900

1000

Properties of while loop

A conditional expression is used to check the condition. The statements defined inside the while loop will repeatedly execute until the given condition fails.
The condition will be true if it returns 0. The condition will be false if it returns any non-zero number.
In while loop, the condition expression is compulsory.
Running a while loop without a body is possible.
We can have more than one conditional expression in while loop.
If the loop body contains only one statement, then the braces are optional.

Example 1

#include<stdio.h>
Void main ()
{
Int j = 1;
While(j+=2,j<=10)
{
Printf("%d ",j);
}
Printf("%d",j);
}

Output

3 5 7 9 11

Example 2

#include<stdio.h>
Void main ()
{
While()
{
Printf("hello Javatpoint");
}
}

Output

Compile time error: while loop can't be empty

Example 3

#include<stdio.h>
Void main ()
{
Int x = 10, y = 2;
While(x+y-1)
{
Printf("%d %d",x--,y--);
}
}

Output

Infinite loop

Infinitive while loop in C

If the expression passed in while loop results in any non-zero value then the loop will run the infinite number of times.

While(1){
//statement
}

For loop in C

The for loop in C language is used to iterate the statements or a part of the program several times. It is frequently used to traverse the data structures like the array and linked list.

Syntax of for loop in C

The syntax of for loop in c language is given below:

For(Expression 1; Expression 2; Expression 3){
//code to be executed
}

Flowchart of for loop in C

C for loop Examples

Let's see the simple program of for loop that prints table of 1.

#include<stdio.h>
Int main(){
Int i=0;
For(i=1;i<=10;i++){
Printf("%d \n",i);
}
Return 0;
}

Output

C Program: Print table for the given number using C for loop

#include<stdio.h>
Int main(){
Int i=1,number=0;
Printf("Enter a number: ");
Scanf("%d",&number);
For(i=1;i<=10;i++){
Printf("%d \n",(number*i));
}
Return 0;
}

Output

Enter a number: 2

Enter a number: 1000

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

Properties of Expression 1

The expression represents the initialization of the loop variable.
We can initialize more than one variable in Expression 1.
Expression 1 is optional.
In C, we can not declare the variables in Expression 1. However, It can be an exception in some compilers.

Example 1

#include <stdio.h>
Int main()
{
Int a,b,c;
For(a=0,b=12,c=23;a<2;a++)
{
Printf("%d ",a+b+c);
}
}

Output

35 36

Example 2

#include <stdio.h>
Int main()
{
Int i=1;
For(;i<5;i++)
{
Printf("%d ",i);
}
}

Output

1 2 3 4

Properties of Expression 2

Expression 2 is a conditional expression. It checks for a specific condition to be satisfied. If it is not, the loop is terminated.
Expression 2 can have more than one condition. However, the loop will iterate until the last condition becomes false. Other conditions will be treated as statements.
Expression 2 is optional.
Expression 2 can perform the task of expression 1 and expression 3. That is, we can initialize the variable as well as update the loop variable in expression 2 itself.
We can pass zero or non-zero value in expression 2. However, in C, any non-zero value is true, and zero is false by default.

Example 1

#include <stdio.h>
Int main()
{
Int i;
For(i=0;i<=4;i++)
{
Printf("%d ",i);
}
}

Output

0 1 2 3 4

Example 2

#include <stdio.h>
Int main()
{
Int i,j,k;
For(i=0,j=0,k=0;i<4,k<8,j<10;i++)
{
Printf("%d %d %d\n",i,j,k);
j+=2;
k+=3;
}
}

Output

0 0 0

1 2 3

2 4 6

3 6 9

4 8 12

Example 3

#include <stdio.h>
Int main()
{
Int i;
For(i=0;;i++)
{
Printf("%d",i);
}
}

Output

Infinite loop

Properties of Expression 3

Expression 3 is used to update the loop variable.
We can update more than one variable at the same time.
Expression 3 is optional.

Example 1

#include<stdio.h>
Void main ()
{
Int i=0,j=2;
For(i = 0;i<5;i++,j=j+2)
{
Printf("%d %d\n",i,j);
}
}

Output

0 2

1 4

2 6

3 8

4 10

Loop body

The braces {} are used to define the scope of the loop. However, if the loop contains only one statement, then we don't need to use braces. A loop without a body is possible. The braces work as a block separator, i.e., the value variable declared inside for loop is valid only for that block and not outside. Consider the following example.

#include<stdio.h>
Void main ()
{
Int i;
For(i=0;i<10;i++)
{
Int i = 20;
Printf("%d ",i);
}
}

Output

20 20 20 20 20 20 20 20 20 20

Infinitive for loop in C

To make a for loop infinite, we need not give any expression in the syntax. Instead of that, we need to provide two semicolons to validate the syntax of the for loop. This will work as an infinite for loop.

#include<stdio.h>
Void main ()
{
For(;;)
{
Printf("welcome to javatpoint");
}
}

If you run this program, you will see above statement infinite times.

Nested Loops in C

C supports nesting of loops in C. Nesting of loops is the feature in C that allows the looping of statements inside another loop. Let's observe an example of nesting loops in C.

Any number of loops can be defined inside another loop, i.e., there is no restriction for defining any number of loops. The nesting level can be defined at n times. You can define any type of loop inside another loop; for example, you can define 'while' loop inside a 'for' loop.

Syntax of Nested loop

Outer_loop
{
Inner_loop
{
// inner loop statements.
}
// outer loop statements.
}

Outer_loop and Inner_loop are the valid loops that can be a 'for' loop, 'while' loop or 'do-while' loop.

Nested for loop

The nested for loop means any type of loop which is defined inside the 'for' loop.

For (initialization; condition; update)
{
For(initialization; condition; update)
{
// inner loop statements.
}
// outer loop statements.
}

Example of nested for loop

#include <stdio.h>
Int main()
{
Int n;// variable declaration
Printf("Enter the value of n :");
// Displaying the n tables.
For(int i=1;i<=n;i++) // outer loop
{
For(int j=1;j<=10;j++) // inner loop
{
Printf("%d\t",(i*j)); // printing the value.
}
Printf("\n");
}

Explanation of the above code

First, the 'i' variable is initialized to 1 and then program control passes to the i<=n.
The program control checks whether the condition 'i<=n' is true or not.
If the condition is true, then the program control passes to the inner loop.
The inner loop will get executed until the condition is true.
After the execution of the inner loop, the control moves back to the update of the outer loop, i.e., i++.
After incrementing the value of the loop counter, the condition is checked again, i.e., i<=n.
If the condition is true, then the inner loop will be executed again.
This process will continue until the condition of the outer loop is true.

Output:

Nested while loop

The nested while loop means any type of loop which is defined inside the 'while' loop.

While(condition)
{
While(condition)
{
// inner loop statements.
}
// outer loop statements.
}

Example of nested while loop

#include <stdio.h>
Int main()
{
Int rows; // variable declaration
Int columns; // variable declaration
Int k=1; // variable initialization
Printf("Enter the number of rows :"); // input the number of rows.
Scanf("%d",&rows);
Printf("\nEnter the number of columns :"); // input the number of columns.
Scanf("%d",&columns);
Int a[rows][columns]; //2d array declaration
Int i=1;
While(i<=rows) // outer loop
{
Int j=1;
While(j<=columns) // inner loop
{
Printf("%d\t",k); // printing the value of k.
k++; // increment counter
j++;
}
i++;
Printf("\n");
}
}

Explanation of the above code.

We have created the 2d array, i.e., int a[rows][columns].
The program initializes the 'i' variable by 1.
Now, control moves to the while loop, and this loop checks whether the condition is true, then the program control moves to the inner loop.
After the execution of the inner loop, the control moves to the update of the outer loop, i.e., i++.
After incrementing the value of 'i', the condition (i<=rows) is checked.
If the condition is true, the control then again moves to the inner loop.
This process continues until the condition of the outer loop is true.

Output:

Nested do..while loop

The nested do..while loop means any type of loop which is defined inside the 'do..while' loop.

Do
{
Do
{
// inner loop statements.
}while(condition);
// outer loop statements.
}while(condition);

Example of nested do..while loop.

#include <stdio.h>
Int main()
{
/*printing the pattern
********
********
********
******** */
Int i=1;
Do // outer loop
{
Int j=1;
Do // inner loop
{
Printf("*");
j++;
}while(j<=8);
Printf("\n");
i++;
}while(i<=4);
}

Output:

Explanation of the above code.

First, we initialize the outer loop counter variable, i.e., 'i' by 1.
As we know that the do..while loop executes once without checking the condition, so the inner loop is executed without checking the condition in the outer loop.
After the execution of the inner loop, the control moves to the update of the i++.
When the loop counter value is incremented, the condition is checked. If the condition in the outer loop is true, then the inner loop is executed.
This process will continue until the condition in the outer loop is true.

Infinite Loop in C

What is infinite loop?

An infinite loop is a looping construct that does not terminate the loop and executes the loop forever. It is also called an indefinite loop or an endless loop. It either produces a continuous output or no output.

When to use an infinite loop

An infinite loop is useful for those applications that accept the user input and generate the output continuously until the user exits from the application manually. In the following situations, this type of loop can be used:

All the operating systems run in an infinite loop as it does not exist after performing some task. It comes out of an infinite loop only when the user manually shuts down the system.
All the servers run in an infinite loop as the server responds to all the client requests. It comes out of an indefinite loop only when the administrator shuts down the server manually.
All the games also run in an infinite loop. The game will accept the user requests until the user exits from the game.

We can create an infinite loop through various loop structures. The following are the loop structures through which we will define the infinite loop:

For loop
While loop
Do-while loop
Go to statement
C macros

For loop

Let's see the infinite 'for' loop. The following is the definition for the infinite for loop:

For(; ;)
{
// body of the for loop.
}

As we know that all the parts of the 'for' loop are optional, and in the above for loop, we have not mentioned any condition; so, this loop will execute infinite times.

Let's understand through an example.

#include <stdio.h>
Int main()
{
For(;;)
{
Printf("Hello javatpoint");
}
Return 0;
}

In the above code, we run the 'for' loop infinite times, so "Hello javatpoint" will be displayed infinitely.

Output

While loop

Now, we will see how to create an infinite loop using a while loop. The following is the definition for the infinite while loop:

While(1)
{
// body of the loop..
}

In the above while loop, we put '1' inside the loop condition. As we know that any non-zero integer represents the true condition while '0' represents the false condition.

Let's look at a simple example.

#include <stdio.h>
Int main()
{
Int i=0;
While(1)
{
i++;
Printf("i is :%d",i);
}
Return 0;
}

In the above code, we have defined a while loop, which runs infinite times as it does not contain any condition. The value of 'i' will be updated an infinite number of times.

Output

Do..while loop

The do..while loop can also be used to create the infinite loop. The following is the syntax to create the infinite do..while loop.

Do
{
// body of the loop..
}while(1);

The above do..while loop represents the infinite condition as we provide the '1' value inside the loop condition. As we already know that non-zero integer represents the true condition, so this loop will run infinite times.

Goto statement

We can also use the goto statement to define the infinite loop.

Infinite_loop;
// body statements.
Goto infinite_loop;

In the above code, the goto statement transfers the control to the infinite loop.

Macros

We can also create the infinite loop with the help of a macro constant. Let's understand through an example.

#include <stdio.h>
#define infinite for(;;)
Int main()
{
Infinite
{
Printf("hello");
}
Return 0;
}

In the above code, we have defined a macro named as 'infinite', and its value is 'for(;;)'. Whenever the word 'infinite' comes in a program then it will be replaced with a 'for(;;)'.

Output

Till now, we have seen various ways to define an infinite loop. However, we need some approach to come out of the infinite loop. In order to come out of the infinite loop, we can use the break statement.

Let's understand through an example.

#include <stdio.h>
Int main()
{
Char ch;
While(1)
{
Ch=getchar();
If(ch=='n')
{
Break;
}
Printf("hello");
}
Return 0;
}

In the above code, we have defined the while loop, which will execute an infinite number of times until we press the key 'n'. We have added the 'if' statement inside the while loop. The 'if' statement contains the break keyword, and the break keyword brings control out of the loop.

Unintentional infinite loops

Sometimes the situation arises where unintentional infinite loops occur due to the bug in the code. If we are the beginners, then it becomes very difficult to trace them. Below are some measures to trace an unintentional infinite loop:

We should examine the semicolons carefully. Sometimes we put the semicolon at the wrong place, which leads to the infinite loop.

#include <stdio.h>
Int main()
{
Int i=1;
While(i<=10);
{
Printf("%d", i);
i++;
}
Return 0;
}

In the above code, we put the semicolon after the condition of the while loop which leads to the infinite loop. Due to this semicolon, the internal body of the while loop will not execute.

We should check the logical conditions carefully. Sometimes by mistake, we place the assignment operator (=) instead of a relational operator (= =).

#include <stdio.h>
Int main()
{
Char ch='n';
While(ch='y')
{
Printf("hello");
}
Return 0;
}

In the above code, we use the assignment operator (ch='y') which leads to the execution of loop infinite number of times.

We use the wrong loop condition which causes the loop to be executed indefinitely.

#include <stdio.h>
Int main()
{
For(int i=1;i>=1;i++)
{
Printf("hello");
}
Return 0;
}

The above code will execute the 'for loop' infinite number of times. As we put the condition (i>=1), which will always be true for every condition, it means that "hello" will be printed infinitely.

We should be careful when we are using the break keyword in the nested loop because it will terminate the execution of the nearest loop, not the entire loop.

#include <stdio.h>
Int main()
{
While(1)
{
For(int i=1;i<=10;i++)
{
If(i%2==0)
{
Break;
}
}
}
Return 0;
}

In the above code, the while loop will be executed an infinite number of times as we use the break keyword in an inner loop. This break keyword will bring the control out of the inner loop, not from the outer loop.

We should be very careful when we are using the floating-point value inside the loop as we cannot underestimate the floating-point errors.

#include <stdio.h>
Int main()
{
Float x = 3.0;
While (x != 4.0) {
Printf("x = %f\n", x);
x += 0.1;
}
Return 0;
}

In the above code, the loop will run infinite times as the computer represents a floating-point value as a real value. The computer will represent the value of 4.0 as 3.999999 or 4.000001, so the condition (x !=4.0) will never be false. The solution to this problem is to write the condition as (k<=4.0).

C break statement

The break is a keyword in C which is used to bring the program control out of the loop. The break statement is used inside loops or switch statement. The break statement breaks the loop one by one, i.e., in the case of nested loops, it breaks the inner loop first and then proceeds to outer loops. The break statement in C can be used in the following two scenarios:

With switch case
With loop

Syntax:

//loop or switch case
Break;

Flowchart of break in c

Example

#include<stdio.h>
#include<stdlib.h>
Void main ()
{
Int i;
For(i = 0; i<10; i++)
{
Printf("%d ",i);
If(i == 5)
Break;
}
Printf("came outside of loop i = %d",i);
}

Output

0 1 2 3 4 5 came outside of loop i = 5

Example of C break statement with switch case

C break statement with the nested loop

In such case, it breaks only the inner loop, but not outer loop.

#include<stdio.h>
Int main(){
Int i=1,j=1;//initializing a local variable
For(i=1;i<=3;i++){
For(j=1;j<=3;j++){
Printf("%d &d\n",i,j);
If(i==2 && j==2){
Break;//will break loop of j only
}
}//end of for loop
Return 0;
}

Output

1 1

1 2

1 3

2 1

2 2

3 1

3 2

3 3

As you can see the output on the console, 2 3 is not printed because there is a break statement after printing i==2 and j==2. But 3 1, 3 2 and 3 3 are printed because the break statement is used to break the inner loop only.

Break statement with while loop

Consider the following example to use break statement inside while loop.

#include<stdio.h>
Void main ()
{
Int i = 0;
While(1)
{
Printf("%d ",i);
i++;
If(i == 10)
Break;
}
Printf("came out of while loop");
}

Output

0 1 2 3 4 5 6 7 8 9 came out of while loop

Break statement with do-while loop

Consider the following example to use the break statement with a do-while loop.

#include<stdio.h>
Void main ()
{
Int n=2,i,choice;
Do
{
i=1;
While(i<=10)
{
Printf("%d X %d = %d\n",n,i,n*i);
i++;
}
Printf("do you want to continue with the table of %d , enter any non-zero value to continue.",n+1);
Scanf("%d",&choice);
If(choice == 0)
{
Break;
}
n++;
}while(1);
}

Output

2 X 1 = 2

2 X 2 = 4

2 X 3 = 6

2 X 4 = 8

2 X 5 = 10

2 X 6 = 12

2 X 7 = 14

2 X 8 = 16

2 X 9 = 18

2 X 10 = 20

Do you want to continue with the table of 3 , enter any non-zero value to continue.1

3 X 1 = 3

3 X 2 = 6

3 X 3 = 9

3 X 4 = 12

3 X 5 = 15

3 X 6 = 18

3 X 7 = 21

3 X 8 = 24

3 X 9 = 27

3 X 10 = 30

Do you want to continue with the table of 4 , enter any non-zero value to continue.0

C continue statement

The continue statement in C language is used to bring the program control to the beginning of the loop. The continue statement skips some lines of code inside the loop and continues with the next iteration. It is mainly used for a condition so that we can skip some code for a particular condition.

Syntax:

//loop statements
Continue;
//some lines of the code which is to be skipped

Continue statement example 1

#include<stdio.h>
Void main ()
{
Int i = 0;
While(i!=10)
{
Printf("%d", i);
Continue;
i++;
}
}

Output

Infinite loop

Continue statement example 2

#include<stdio.h>
Int main(){
Int i=1;//initializing a local variable
//starting a loop from 1 to 10
For(i=1;i<=10;i++){
If(i==5){//if value of i is equal to 5, it will continue the loop
Continue;
}
Printf("%d \n",i);
}//end of for loop
Return 0;
}

Output

As you can see, 5 is not printed on the console because loop is continued at i==5.

C continue statement with inner loop

In such case, C continue statement continues only inner loop, but not outer loop.

#include<stdio.h>
Int main(){
Int i=1,j=1;//initializing a local variable
For(i=1;i<=3;i++){
For(j=1;j<=3;j++){
If(i==2 && j==2){
Continue;//will continue loop of j only
}
Printf("%d %d\n",i,j);
}
}//end of for loop
Return 0;
}

Output

1 1

1 2

1 3

2 1

2 3

3 1

3 2

3 3

As you can see, 2 2 is not printed on the console because inner loop is continued at i==2 and j==2.

C goto statement

The goto statement is known as jump statement in C. As the name suggests, goto is used to transfer the program control to a predefined label. The goto statment can be used to repeat some part of the code for a particular condition. It can also be used to break the multiple loops which can't be done by using a single break statement. However, using goto is avoided these days since it makes the program less readable and complecated.

Syntax:

Label:
//some part of the code;
Goto label;

Goto example

Let's see a simple example to use goto statement in C language.

#include <stdio.h>
Int main()
{
Int num,i=1;
Printf("Enter the number whose table you want to print?");
Scanf("%d",&num);
Table:
Printf("%d x %d = %d\n",num,i,num*i);
i++;
If(i<=10)
Goto table;
}

Output:

Enter the number whose table you want to print?10

10 x 1 = 10

10 x 2 = 20

10 x 3 = 30

10 x 4 = 40

10 x 5 = 50

10 x 6 = 60

10 x 7 = 70

10 x 8 = 80

10 x 9 = 90

10 x 10 = 100

When should we use goto?

The only condition in which using goto is preferable is when we need to break the multiple loops using a single statement at the same time. Consider the following example.

#include <stdio.h>
Int main()
{
Int i, j, k;
For(i=0;i<10;i++)
{
For(j=0;j<5;j++)
{
For(k=0;k<3;k++)
{
Printf("%d %d %d\n",i,j,k);
If(j == 3)
{
Goto out;
}
}
}
}
Out:
Printf("came out of the loop");
}

0 0 0

0 0 1

0 0 2

0 1 0

0 1 1

0 1 2

0 2 0

0 2 1

0 2 2

0 3 0

Came out of the loop

3.8 Arrays

An array is defined as the collection of similar type of data items stored at contiguous memory locations. Arrays are the derived data type in C programming language which can store the primitive type of data such as int, char, double, float, etc. It also has the capability to store the collection of derived data types, such as pointers, structure, etc. The array is the simplest data structure where each data element can be randomly accessed by using its index number.

C array is beneficial if you have to store similar elements. For example, if we want to store the marks of a student in 6 subjects, then we don't need to define different variables for the marks in the different subject. Instead of that, we can define an array which can store the marks in each subject at the contiguous memory locations.

By using the array, we can access the elements easily. Only a few lines of code are required to access the elements of the array.

Properties of Array

The array contains the following properties.

Each element of an array is of same data type and carries the same size, i.e., int = 4 bytes.
Elements of the array are stored at contiguous memory locations where the first element is stored at the smallest memory location.
Elements of the array can be randomly accessed since we can calculate the address of each element of the array with the given base address and the size of the data element.

Advantage of C Array

1) Code Optimization: Less code to the access the data.

2) Ease of traversing: By using the for loop, we can retrieve the elements of an array easily.

3) Ease of sorting: To sort the elements of the array, we need a few lines of code only.

4) Random Access: We can access any element randomly using the array.

Disadvantage of C Array

1) Fixed Size: Whatever size, we define at the time of declaration of the array, we can't exceed the limit. So, it doesn't grow the size dynamically like LinkedList which we will learn later.

Declaration of C Array

We can declare an array in the c language in the following way.

Data_type array_name[array_size];

Now, let us see the example to declare the array.

Int marks[5];

Here, int is the data_type, marks are the array_name, and 5 is the array_size.

Initialization of C Array

The simplest way to initialize an array is by using the index of each element. We can initialize each element of the array by using the index. Consider the following example.

Marks[0]=80;//initialization of array
Marks[1]=60;
Marks[2]=70;
Marks[3]=85;
Marks[4]=75;

C array example

#include<stdio.h>
Int main(){
Int i=0;
Int marks[5];//declaration of array
Marks[0]=80;//initialization of array
Marks[1]=60;
Marks[2]=70;
Marks[3]=85;
Marks[4]=75;
//traversal of array
For(i=0;i<5;i++){
Printf("%d \n",marks[i]);
}//end of for loop
Return 0;
}

Output

C Array: Declaration with Initialization

We can initialize the c array at the time of declaration. Let's see the code.

Int marks[5]={20,30,40,50,60};

In such case, there is no requirement to define the size. So it may also be written as the following code.

Int marks[]={20,30,40,50,60};

Let's see the C program to declare and initialize the array in C.

#include<stdio.h>
Int main(){
Int i=0;
Int marks[5]={20,30,40,50,60};//declaration and initialization of array
//traversal of array
For(i=0;i<5;i++){
Printf("%d \n",marks[i]);
}
Return 0;
}

Output

C Array Example: Sorting an array

In the following program, we are using bubble sort method to sort the array in ascending order.

#include<stdio.h>
Void main ()
{
Int i, j,temp;
Int a[10] = { 10, 9, 7, 101, 23, 44, 12, 78, 34, 23};
For(i = 0; i<10; i++)
{
For(j = i+1; j<10; j++)
{
If(a[j] > a[i])
{
Temp = a[i];
a[i] = a[j];
a[j] = temp;
}
}
}
Printf("Printing Sorted Element List ...\n");
For(i = 0; i<10; i++)
{
Printf("%d\n",a[i]);
}
}

Program to print the largest and second largest element of the array.

#include<stdio.h>
Void main ()
{
Int arr[100],i,n,largest,sec_largest;
Printf("Enter the size of the array?");
Scanf("%d",&n);
Printf("Enter the elements of the array?");
For(i = 0; i<n; i++)
{
Scanf("%d",&arr[i]);
}
Largest = arr[0];
Sec_largest = arr[1];
For(i=0;i<n;i++)
{
If(arr[i]>largest)
{
Sec_largest = largest;
Largest = arr[i];
}
Else if (arr[i]>sec_largest && arr[i]!=largest)
{
Sec_largest=arr[i];
}
}
Printf("largest = %d, second largest = %d",largest,sec_largest);
}

3.9 Functions, parameter passing

In c, we can divide a large program into the basic building blocks known as function. The function contains the set of programming statements enclosed by {}. A function can be called multiple times to provide reusability and modularity to the C program. In other words, we can say that the collection of functions creates a program. The function is also known as procedureor subroutinein other programming languages.

Advantage of functions in C

There are the following advantages of C functions.

By using functions, we can avoid rewriting same logic/code again and again in a program.
We can call C functions any number of times in a program and from any place in a program.
We can track a large C program easily when it is divided into multiple functions.
Reusability is the main achievement of C functions.
However, Function calling is always a overhead in a C program.

Function Aspects

There are three aspects of a C function.

Function declarationA function must be declared globally in a c program to tell the compiler about the function name, function parameters, and return type.

Function call Function can be called from anywhere in the program. The parameter list must not differ in function calling and function declaration. We must pass the same number of functions as it is declared in the function declaration.

Function definitionIt contains the actual statements which are to be executed. It is the most important aspect to which the control comes when the function is called. Here, we must notice that only one value can be returned from the function.

SN	C function aspects	Syntax
1	Function declaration	Return_type function_name (argument list);
2	Function call	Function_name (argument_list)
3	Function definition	Return_type function_name (argument list) {function body;}

The syntax of creating function in c language is given below:

Return_type function_name(data_type parameter...){
//code to be executed
}

Types of Functions

There are two types of functions in C programming:

Library Functions: are the functions which are declared in the C header files such as scanf(), printf(), gets(), puts(), ceil(), floor() etc.
User-defined functions: are the functions which are created by the C programmer, so that he/she can use it many times. It reduces the complexity of a big program and optimizes the code.

Return Value

A C function may or may not return a value from the function. If you don't have to return any value from the function, use void for the return type.

Let's see a simple example of C function that doesn't return any value from the function.

Example without return value:

Void hello(){
Printf("hello c");
}

If you want to return any value from the function, you need to use any data type such as int, long, char, etc. The return type depends on the value to be returned from the function.

Let's see a simple example of C function that returns int value from the function.

Example with return value:

Int get(){
Return 10;
}

In the above example, we have to return 10 as a value, so the return type is int. If you want to return floating-point value (e.g., 10.2, 3.1, 54.5, etc), you need to use float as the return type of the method.

Float get(){
Return 10.2;
}

Now, you need to call the function, to get the value of the function.

Different aspects of function calling

A function may or may not accept any argument. It may or may not return any value. Based on these facts, There are four different aspects of function calls.

Function without arguments and without return value
Function without arguments and with return value
Function with arguments and without return value
Function with arguments and with return value

Example for Function without argument and return value

Example 1

#include<stdio.h>
Void printName();
Void main ()
{
Printf("Hello ");
PrintName();
}
Void printName()
{
Printf("Javatpoint");
}

Output

Hello Javatpoint

Example 2

#include<stdio.h>
Void sum();
Void main()
{
Printf("\nGoing to calculate the sum of two numbers:");
Sum();
}
Void sum()
{
Int a,b;
Printf("\nEnter two numbers");
Scanf("%d %d",&a,&b);
Printf("The sum is %d",a+b);
}

Output

Going to calculate the sum of two numbers:

Enter two numbers 10

The sum is 34

Example for Function without argument and with return value

Example 1

#include<stdio.h>
Int sum();
Void main()
{
Int result;
Printf("\nGoing to calculate the sum of two numbers:");
Result = sum();
Printf("%d",result);
}
Int sum()
{
Int a,b;
Printf("\nEnter two numbers");
Scanf("%d %d",&a,&b);
Return a+b;
}

Output

Going to calculate the sum of two numbers:

Enter two numbers 10

The sum is 34

Example 2: program to calculate the area of the square

#include<stdio.h>
Int sum();
Void main()
{
Printf("Going to calculate the area of the square\n");
Float area = square();
Printf("The area of the square: %f\n",area);
}
Int square()
{
Float side;
Printf("Enter the length of the side in meters: ");
Scanf("%f",&side);
Return side * side;
}

Output

Going to calculate the area of the square

Enter the length of the side in meters: 10

The area of the square: 100.000000

Example for Function with argument and without return value

Example 1

#include<stdio.h>
Void sum(int, int);
Void main()
{
Int a,b,result;
Printf("\nGoing to calculate the sum of two numbers:");
Printf("\nEnter two numbers:");
Scanf("%d %d",&a,&b);
Sum(a,b);
}
Void sum(int a, int b)
{
Printf("\nThe sum is %d",a+b);
}

Output

Going to calculate the sum of two numbers:

Enter two numbers 10

The sum is 34

Example 2: program to calculate the average of five numbers.

#include<stdio.h>
Void average(int, int, int, int, int);
Void main()
{
Int a,b,c,d,e;
Printf("\nGoing to calculate the average of five numbers:");
Printf("\nEnter five numbers:");
Scanf("%d %d %d %d %d",&a,&b,&c,&d,&e);
Average(a,b,c,d,e);
}
Void average(int a, int b, int c, int d, int e)
{
Float avg;
Avg = (a+b+c+d+e)/5;
Printf("The average of given five numbers : %f",avg);
}

Output

Going to calculate the average of five numbers:

Enter five numbers:10

The average of given five numbers : 30.000000

Example for Function with argument and with return value

Example 1

#include<stdio.h>
Int sum(int, int);
Void main()
{
Int a,b,result;
Printf("\nGoing to calculate the sum of two numbers:");
Printf("\nEnter two numbers:");
Scanf("%d %d",&a,&b);
Result = sum(a,b);
Printf("\nThe sum is : %d",result);
}
Int sum(int a, int b)
{
Return a+b;
}

Output

Going to calculate the sum of two numbers:

Enter two numbers:10

The sum is : 30

Example 2: Program to check whether a number is even or odd

#include<stdio.h>
Int even_odd(int);
Void main()
{
Int n,flag=0;
Printf("\nGoing to check whether a number is even or odd");
Printf("\nEnter the number: ");
Scanf("%d",&n);
Flag = even_odd(n);
If(flag == 0)
{
Printf("\nThe number is odd");
}
Else
{
Printf("\nThe number is even");
}
}
Int even_odd(int n)
{
If(n%2 == 0)
{
Return 1;
}
Else
{
Return 0;
}
}

Output

Going to check whether a number is even or odd

Enter the number: 100

The number is even

C Library Functions

Library functions are the inbuilt function in C that are grouped and placed at a common place called the library. Such functions are used to perform some specific operations. For example, printf is a library function used to print on the console. The library functions are created by the designers of compilers. All C standard library functions are defined inside the different header files saved with the extension .h. We need to include these header files in our program to make use of the library functions defined in such header files. For example, To use the library functions such as printf/scanf we need to include stdio.h in our program which is a header file that contains all the library functions regarding standard input/output.

The list of mostly used header files is given in the following table.

SN	Header file	Description
1	Stdio.h	This is a standard input/output header file. It contains all the library functions regarding standard input/output.
2	Conio.h	This is a console input/output header file.
3	String.h	It contains all string related library functions like gets(), puts(),etc.
4	Stdlib.h	This header file contains all the general library functions like malloc(), calloc(), exit(), etc.
5	Math.h	This header file contains all the math operations related functions like sqrt(), pow(), etc.
6	Time.h	This header file contains all the time-related functions.
7	Ctype.h	This header file contains all character handling functions.
8	Stdarg.h	Variable argument functions are defined in this header file.
9	Signal.h	All the signal handling functions are defined in this header file.
10	Setjmp.h	This file contains all the jump functions.
11	Locale.h	This file contains locale functions.
12	Errno.h	This file contains error handling functions.
13	Assert.h	This file contains diagnostics functions.

Call by value and Call by reference in C

There are two methods to pass the data into the function in C language, i.e., call by value and call by reference.

Let's understand call by value and call by reference in c language one by one.

Call by value in C

In call by value method, the value of the actual parameters is copied into the formal parameters. In other words, we can say that the value of the variable is used in the function call in the call by value method.
In call by value method, we can not modify the value of the actual parameter by the formal parameter.
In call by value, different memory is allocated for actual and formal parameters since the value of the actual parameter is copied into the formal parameter.
The actual parameter is the argument which is used in the function call whereas formal parameter is the argument which is used in the function definition.

Let's try to understand the concept of call by value in c language by the example given below:

#include<stdio.h>
Void change(int num) {
Printf("Before adding value inside function num=%d \n",num);
Num=num+100;
Printf("After adding value inside function num=%d \n", num);
}
Int main() {
Int x=100;
Printf("Before function call x=%d \n", x);
Change(x);//passing value in function
Printf("After function call x=%d \n", x);
Return 0;
}

Output

Before function call x=100

Before adding value inside function num=100

After adding value inside function num=200

After function call x=100

Call by Value Example: Swapping the values of the two variables

#include <stdio.h>
Void swap(int , int); //prototype of the function
Int main()
{
Int a = 10;
Int b = 20;
Printf("Before swapping the values in main a = %d, b = %d\n",a,b); // printing the value of a and b in main
Swap(a,b);
Printf("After swapping values in main a = %d, b = %d\n",a,b); // The value of actual parameters do not change by changing the formal parameters in call by value, a = 10, b = 20
}
Void swap (int a, int b)
{
Int temp;
Temp = a;
a=b;
b=temp;
Printf("After swapping values in function a = %d, b = %d\n",a,b); // Formal parameters, a = 20, b = 10
}

Output

Before swapping the values in main a = 10, b = 20

After swapping values in function a = 20, b = 10

After swapping values in main a = 10, b = 20

Call by reference in C

In call by reference, the address of the variable is passed into the function call as the actual parameter.
The value of the actual parameters can be modified by changing the formal parameters since the address of the actual parameters is passed.
In call by reference, the memory allocation is similar for both formal parameters and actual parameters. All the operations in the function are performed on the value stored at the address of the actual parameters, and the modified value gets stored at the same address.

Consider the following example for the call by reference.

#include<stdio.h>
Void change(int *num) {
Printf("Before adding value inside function num=%d \n",*num);
(*num) += 100;
Printf("After adding value inside function num=%d \n", *num);
}
Int main() {
Int x=100;
Printf("Before function call x=%d \n", x);
Change(&x);//passing reference in function
Printf("After function call x=%d \n", x);
Return 0;
}

Output

Before function call x=100

Before adding value inside function num=100

After adding value inside function num=200

After function call x=200

Call by reference Example: Swapping the values of the two variables

#include <stdio.h>
Void swap(int *, int *); //prototype of the function
Int main()
{
Int a = 10;
Int b = 20;
Printf("Before swapping the values in main a = %d, b = %d\n",a,b); // printing the value of a and b in main
Swap(&a,&b);
Printf("After swapping values in main a = %d, b = %d\n",a,b); // The values of actual parameters do change in call by reference, a = 10, b = 20
}
Void swap (int *a, int *b)
{
Int temp;
Temp = *a;
*a=*b;
*b=temp;
Printf("After swapping values in function a = %d, b = %d\n",*a,*b); // Formal parameters, a = 20, b = 10
}

Output

Before swapping the values in main a = 10, b = 20

After swapping values in function a = 20, b = 10

After swapping values in main a = 20, b = 10

Difference between call by value and call by reference in c

No.	Call by value	Call by reference
1	A copy of the value is passed into the function	An address of value is passed into the function
2	Changes made inside the function is limited to the function only. The values of the actual parameters do not change by changing the formal parameters.	Changes made inside the function validate outside of the function also. The values of the actual parameters do change by changing the formal parameters.
3	Actual and formal arguments are created at the different memory location	Actual and formal arguments are created at the same memory location

3.10 Recursion, Programming in C using these statements

Recursion is the process which comes into existence when a function calls a copy of itself to work on a smaller problem. Any function which calls itself is called recursive function, and such function calls are called recursive calls. Recursion involves several numbers of recursive calls. However, it is important to impose a termination condition of recursion. Recursion code is shorter than iterative code however it is difficult to understand.

Recursion cannot be applied to all the problem, but it is more useful for the tasks that can be defined in terms of similar subtasks. For Example, recursion may be applied to sorting, searching, and traversal problems.

Generally, iterative solutions are more efficient than recursion since function call is always overhead. Any problem that can be solved recursively, can also be solved iteratively. However, some problems are best suited to be solved by the recursion, for example, tower of Hanoi, Fibonacci series, factorial finding, etc.

In the following example, recursion is used to calculate the factorial of a number.

#include <stdio.h>
Int fact (int);
Int main()
{
Int n,f;
Printf("Enter the number whose factorial you want to calculate?");
Scanf("%d",&n);
f = fact(n);
Printf("factorial = %d",f);
}
Int fact(int n)
{
If (n==0)
{
Return 0;
}
Else if ( n == 1)
{
Return 1;
}
Else
{
Return n*fact(n-1);
}
}

Output

Enter the number whose factorial you want to calculate?5

Factorial = 120

We can understand the above program of the recursive method call by the figure given below:

Recursive Function

A recursive function performs the tasks by dividing it into the subtasks. There is a termination condition defined in the function which is satisfied by some specific subtask. After this, the recursion stops and the final result is returned from the function.

The case at which the function doesn't recur is called the base case whereas the instances where the function keeps calling itself to perform a subtask, is called the recursive case. All the recursive functions can be written using this format.

Pseudocode for writing any recursive function is given below.

If (test_for_base)
{
Return some_value;
}
Else if (test_for_another_base)
{
Return some_another_value;
}
Else
{
// Statements;
Recursive call;
}

Example of recursion in C

Let's see an example to find the nth term of the Fibonacci series.

#include<stdio.h>
Int fibonacci(int);
Void main ()
{
Int n,f;
Printf("Enter the value of n?");
Scanf("%d",&n);
f = fibonacci(n);
Printf("%d",f);
}
Int fibonacci (int n)
{
If (n==0)
{
Return 0;
}
Else if (n == 1)
{
Return 1;
}
Else
{
Return fibonacci(n-1)+fibonacci(n-2);
}
}

Output

Enter the value of n?12

144

Memory allocation of Recursive method

Each recursive call creates a new copy of that method in the memory. Once some data is returned by the method, the copy is removed from the memory. Since all the variables and other stuff declared inside function get stored in the stack, therefore a separate stack is maintained at each recursive call. Once the value is returned from the corresponding function, the stack gets destroyed. Recursion involves so much complexity in resolving and tracking the values at each recursive call. Therefore we need to maintain the stack and track the values of the variables defined in the stack.

Let us consider the following example to understand the memory allocation of the recursive functions.

Int display (int n)
{
If(n == 0)
Return 0; // terminating condition
Else
{
Printf("%d",n);
Return display(n-1); // recursive call
}
}

Explanation

Let us examine this recursive function for n = 4. First, all the stacks are maintained which prints the corresponding value of n until n becomes 0, Once the termination condition is reached, the stacks get destroyed one by one by returning 0 to its calling stack. Consider the following image for more information regarding the stack trace for the recursive functions.

3.11 Structures

Why use structure?

In C, there are cases where we need to store multiple attributes of an entity. It is not necessary that an entity has all the information of one type only. It can have different attributes of different data types. For example, an entity Student may have its name (string), roll number (int), marks (float). To store such type of information regarding an entity student, we have the following approaches:

Construct individual arrays for storing names, roll numbers, and marks.
Use a special data structure to store the collection of different data types.

Let's look at the first approach in detail.

#include<stdio.h>
Void main ()
{
Char names[2][10],dummy; // 2-dimensioanal character array names is used to store the names of the students
Int roll_numbers[2],i;
Float marks[2];
For (i=0;i<3;i++)
{
Printf("Enter the name, roll number, and marks of the student %d",i+1);
Scanf("%s %d %f",&names[i],&roll_numbers[i],&marks[i]);
Scanf("%c",&dummy); // enter will be stored into dummy character at each iteration
}
Printf("Printing the Student details ...\n");
For (i=0;i<3;i++)
{
Printf("%s %d %f\n",names[i],roll_numbers[i],marks[i]);
}
}

Output

Enter the name, roll number, and marks of the student 1Arun 90 91

Enter the name, roll number, and marks of the student 2Varun 91 56

Enter the name, roll number, and marks of the student 3Sham 89 69

Printing the Student details...

Arun 90 91.000000

Varun 91 56.000000

Sham 89 69.000000

The above program may fulfill our requirement of storing the information of an entity student. However, the program is very complex, and the complexity increase with the amount of the input. The elements of each of the array are stored contiguously, but all the arrays may not be stored contiguously in the memory. C provides you with an additional and simpler approach where you can use a special data structure, i.e., structure, in which, you can group all the information of different data type regarding an entity.

What is Structure

Structure in c is a user-defined data type that enables us to store the collection of different data types. Each element of a structure is called a member. Structures ca; simulate the use of classes and templates as it can store various information

The ,struct keyword is used to define the structure. Let's see the syntax to define the structure in c.

Struct structure_name
{
Data_type member1;
Data_type member2;
.
.
Data_type memeberN;
};

Let's see the example to define a structure for an entity employee in c.

Struct employee
{ int id;
Char name[20];
Float salary;
};

The following image shows the memory allocation of the structure employee that is defined in the above example.

Here, struct is the keyword; employee is the name of the structure; id, name, and salary are the members or fields of the structure. Let's understand it by the diagram given below:

Declaring structure variable

We can declare a variable for the structure so that we can access the member of the structure easily. There are two ways to declare structure variable:

By struct keyword within main() function
By declaring a variable at the time of defining the structure.

1st way:

Let's see the example to declare the structure variable by struct keyword. It should be declared within the main function.

Struct employee
{ int id;
Char name[50];
Float salary;
};

Now write given code inside the main() function.

Struct employee e1, e2;

The variables e1 and e2 can be used to access the values stored in the structure. Here, e1 and e2 can be treated in the same way as the objects in C++ and Java.

2nd way:

Let's see another way to declare variable at the time of defining the structure.

Struct employee
{ int id;
Char name[50];
Float salary;
}e1,e2;

Which approach is good

If number of variables are not fixed, use the 1st approach. It provides you the flexibility to declare the structure variable many times.

If no. Of variables are fixed, use 2nd approach. It saves your code to declare a variable in main() function.

Accessing members of the structure

There are two ways to access structure members:

By . (member or dot operator)
By -> (structure pointer operator)

Let's see the code to access the id member of p1 variable by. (member) operator.

p1.id

C Structure example

Let's see a simple example of structure in C language.

#include<stdio.h>
#include <string.h>
Struct employee
{ int id;
Char name[50];
}e1; //declaring e1 variable for structure
Int main( )
{
//store first employee information
e1.id=101;
Strcpy(e1.name, "Sonoo Jaiswal");//copying string into char array
//printing first employee information
Printf( "employee 1 id : %d\n", e1.id);
Printf( "employee 1 name : %s\n", e1.name);
Return 0;
}

Output:

Employee 1 id : 101

Employee 1 name : Sonoo Jaiswal

Let's see another example of the structure in C language to store many employees information.

#include<stdio.h>
#include <string.h>
Struct employee
{ int id;
Char name[50];
Float salary;
}e1,e2; //declaring e1 and e2 variables for structure
Int main( )
{
//store first employee information
e1.id=101;
Strcpy(e1.name, "Sonoo Jaiswal");//copying string into char array
e1.salary=56000;
//store second employee information
e2.id=102;
Strcpy(e2.name, "James Bond");
e2.salary=126000;
//printing first employee information
Printf( "employee 1 id : %d\n", e1.id);
Printf( "employee 1 name : %s\n", e1.name);
Printf( "employee 1 salary : %f\n", e1.salary);
//printing second employee information
Printf( "employee 2 id : %d\n", e2.id);
Printf( "employee 2 name : %s\n", e2.name);
Printf( "employee 2 salary : %f\n", e2.salary);
Return 0;
}

Output:

Employee 1 id : 101

Employee 1 name : Sonoo Jaiswal

Employee 1 salary : 56000.000000

Employee 2 id : 102

Employee 2 name : James Bond

Employee 2 salary : 126000.000000

3.12 Files and Multi file handling

In programming, we may require some specific input data to be generated several numbers of times. Sometimes, it is not enough to only display the data on the console. The data to be displayed may be very large, and only a limited amount of data can be displayed on the console, and since the memory is volatile, it is impossible to recover the programmatically generated data again and again. However, if we need to do so, we may store it onto the local file system which is volatile and can be accessed every time. Here, comes the need of file handling in C.

File handling in C enables us to create, update, read, and delete the files stored on the local file system through our C program. The following operations can be performed on a file.

Creation of the new file
Opening an existing file
Reading from the file
Writing to the file
Deleting the file

Functions for file handling

There are many functions in the C library to open, read, write, search and close the file. A list of file functions are given below:

No.	Function	Description
1	Fopen()	Opens new or existing file
2	Fprintf()	Write data into the file
3	Fscanf()	Reads data from the file
4	Fputc()	Writes a character into the file
5	Fgetc()	Reads a character from file
6	Fclose()	Closes the file
7	Fseek()	Sets the file pointer to given position
8	Fputw()	Writes an integer to file
9	Fgetw()	Reads an integer from file
10	Ftell()	Returns current position
11	Rewind()	Sets the file pointer to the beginning of the file

Opening File: fopen()

We must open a file before it can be read, write, or update. The fopen() function is used to open a file. The syntax of the fopen() is given below.

FILE *fopen( const char * filename, const char * mode );

The fopen() function accepts two parameters:

The file name (string). If the file is stored at some specific location, then we must mention the path at which the file is stored. For example, a file name can be like "c://some_folder/some_file.ext".
The mode in which the file is to be opened. It is a string.

We can use one of the following modes in the fopen() function.

Mode	Description
r	Opens a text file in read mode
w	Opens a text file in write mode
a	Opens a text file in append mode
r+	Opens a text file in read and write mode
w+	Opens a text file in read and write mode
a+	Opens a text file in read and write mode
Rb	Opens a binary file in read mode
Wb	Opens a binary file in write mode
Ab	Opens a binary file in append mode
Rb+	Opens a binary file in read and write mode
Wb+	Opens a binary file in read and write mode
Ab+	Opens a binary file in read and write mode

The fopen function works in the following way.

Firstly, It searches the file to be opened.
Then, it loads the file from the disk and place it into the buffer. The buffer is used to provide efficiency for the read operations.
It sets up a character pointer which points to the first character of the file.

Consider the following example which opens a file in write mode.

#include<stdio.h>
Void main( )
{
FILE *fp ;
Char ch ;
Fp = fopen("file_handle.c","r") ;
While ( 1 )
{
Ch = fgetc ( fp ) ;
If ( ch == EOF )
Break ;
Printf("%c",ch) ;
}
Fclose (fp ) ;
}

Output

The content of the file will be printed.

#include;

Void main( )

{

FILE *fp; // file pointer

Char ch;

Fp = fopen("file_handle.c","r");

While ( 1 )

{

Ch = fgetc ( fp ); //Each character of the file is read and stored in the character file.

If ( ch == EOF )

Break;

Printf("%c",ch);

}

Fclose (fp );

}

Closing File: fclose()

The fclose() function is used to close a file. The file must be closed after performing all the operations on it. The syntax of fclose() function is given below:

Int fclose( FILE *fp );

C fprintf() and fscanf()

Writing File : fprintf() function

The fprintf() function is used to write set of characters into file. It sends formatted output to a stream.

Syntax:

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

Example:

#include <stdio.h>
Main(){
FILE *fp;
Fp = fopen("file.txt", "w");//opening file
Fprintf(fp, "Hello file by fprintf...\n");//writing data into file
Fclose(fp);//closing file
}

Reading File : fscanf() function

The fscanf() function is used to read set of characters from file. It reads a word from the file and returns EOF at the end of file.

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...

C File Example: Storing employee information

Let's see a file handling example to store employee information as entered by user from console. We are going to store id, name and salary of the employee.

#include <stdio.h>
Void main()
{
FILE *fptr;
Int id;
Char name[30];
Float salary;
Fptr = fopen("emp.txt", "w+");/* open for writing */
If (fptr == NULL)
{
Printf("File does not exists \n");
Return;
}
Printf("Enter the id\n");
Scanf("%d", &id);
Fprintf(fptr, "Id= %d\n", id);
Printf("Enter the name \n");
Scanf("%s", name);
Fprintf(fptr, "Name= %s\n", name);
Printf("Enter the salary\n");
Scanf("%f", &salary);
Fprintf(fptr, "Salary= %.2f\n", salary);
Fclose(fptr);
}

Output:

Enter the id

Enter the name

Sonoo

Enter the salary

120000

Now open file from current directory. For windows operating system, go to TC\bin directory, you will see emp.txt file. It will have following information.

Emp.txt

Id= 1

Name= sonoo

Salary= 120000

C fputc() and fgetc()

Writing File : fputc() function

The fputc() function is used to write a single character into file. It outputs a character to a stream.

Syntax:

Int fputc(int c, FILE *stream)

Example:

#include <stdio.h>
Main(){
FILE *fp;
Fp = fopen("file1.txt", "w");//opening file
Fputc('a',fp);//writing single character into file
Fclose(fp);//closing file
}

File1.txt

Reading File : fgetc() function

The fgetc() function returns a single character from the file. It gets a character from the stream. It returns EOF at the end of file.

Syntax:

Int fgetc(FILE *stream)

Example:

#include<stdio.h>
#include<conio.h>
Void main(){
FILE *fp;
Char c;
Clrscr();
Fp=fopen("myfile.txt","r");
While((c=fgetc(fp))!=EOF){
Printf("%c",c);
}
Fclose(fp);
Getch();
}

Myfile.txt

This is simple text message

C fputs() and fgets()

The fputs() and fgets() in C programming are used to write and read string from stream. Let's see examples of writing and reading file using fgets() and fgets() functions.

Writing File : fputs() function

The fputs() function writes a line of characters into file. It outputs string to a stream.

Syntax:

Int fputs(const char *s, FILE *stream)

Example:

#include<stdio.h>
#include<conio.h>
Void main(){
FILE *fp;
Clrscr();
Fp=fopen("myfile2.txt","w");
Fputs("hello c programming",fp);
Fclose(fp);
Getch();
}

Myfile2.txt

Hello c programming

Reading File : fgets() function

The fgets() function reads a line of characters from file. It gets string from a stream.

Syntax:

Char* fgets(char *s, int n, FILE *stream)

Example:

#include<stdio.h>
#include<conio.h>
Void main(){
FILE *fp;
Char text[300];
Clrscr();
Fp=fopen("myfile2.txt","r");
Printf("%s",fgets(text,200,fp));
Fclose(fp);
Getch();
}

Output:

Hello c programming

C fseek() function

The fseek() function is used to set the file pointer to the specified offset. It is used to write data into file at desired location.

Syntax:

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

There are 3 constants used in the fseek() function for whence: 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);
}

Myfile.txt

This is sonoo jaiswal

3.13 Pointers

The pointer in C language is a variable which stores the address of another variable. This variable can be of type int, char, array, function, or any other pointer. The size of the pointer depends on the architecture. However, in 32-bit architecture the size of a pointer is 2 byte.

Consider the following example to define a pointer which stores the address of an integer.

Int n = 10;
Int* p = &n; // Variable p of type pointer is pointing to the address of the variable n of type integer.

Declaring a pointer

The pointer in c language can be declared using * (asterisk symbol). It is also known as indirection pointer used to dereference a pointer.

Int *a;//pointer to int
Char *c;//pointer to char

Pointer Example

An example of using pointers to print the address and value is given below.

As you can see in the above figure, pointer variable stores the address of number variable, i.e., fff4. The value of number variable is 50. But the address of pointer variable p is aaa3.

By the help of * (indirection operator), we can print the value of pointer variable p.

Let's see the pointer example as explained for the above figure.

#include<stdio.h>
Int main(){
Int number=50;
Int *p;
p=&number;//stores the address of number variable
Printf("Address of p variable is %x \n",p); // p contains the address of the number therefore printing p gives the address of number.
Printf("Value of p variable is %d \n",*p); // As we know that * is used to dereference a pointer therefore if we print *p, we will get the value stored at the address contained by p.
Return 0;
}

Output

Address of number variable is fff4

Address of p variable is fff4

Value of p variable is 50

Pointer to array

Int arr[10];
Int *p[10]=&arr; // Variable p of type pointer is pointing to the address of an integer array arr.

Pointer to a function

Void show (int);
Void(*p)(int) = &display; // Pointer p is pointing to the address of a function

Pointer to structure

Struct st {
Int i;
Float f;
}ref;
Struct st *p = &ref;

Advantage of pointer

1) Pointer reduces the code and improves the performance, it is used to retrieving strings, trees, etc. and used with arrays, structures, and functions.

2) We can return multiple values from a function using the pointer.

3) It makes you able to access any memory location in the computer's memory.

Usage of pointer

There are many applications of pointers in c language.

1) Dynamic memory allocation

In c language, we can dynamically allocate memory using malloc() and calloc() functions where the pointer is used.

2) Arrays, Functions, and Structures

Pointers in c language are widely used in arrays, functions, and structures. It reduces the code and improves the performance.

Address Of (&) Operator

The address of operator '&' returns the address of a variable. But, we need to use %u to display the address of a variable.

#include<stdio.h>
Int main(){
Int number=50;
Printf("value of number is %d, address of number is %u",number,&number);
Return 0;
}

Output

Value of number is 50, address of number is fff4

NULL Pointer

A pointer that is not assigned any value but NULL is known as the NULL pointer. If you don't have any address to be specified in the pointer at the time of declaration, you can assign NULL value. It will provide a better approach.

Int *p=NULL;

In the most libraries, the value of the pointer is 0 (zero).

Pointer Program to swap two numbers without using the 3rd variable.

#include<stdio.h>
Int main(){
Int a=10,b=20,*p1=&a,*p2=&b;
Printf("Before swap: *p1=%d *p2=%d",*p1,*p2);
*p1=*p1+*p2;
*p2=*p1-*p2;
*p1=*p1-*p2;
Printf("\nAfter swap: *p1=%d *p2=%d",*p1,*p2);
Return 0;
}

Output

Before swap: *p1=10 *p2=20

After swap: *p1=20 *p2=10

Reading complex pointers

There are several things which must be taken into the consideration while reading the complex pointers in C. Lets see the precedence and associativity of the operators which are used regarding pointers.

Operator	Precedence	Associativity
(), []	1	Left to right
*, identifier	2	Right to left
Data type	3	-

Here,we must notice that,

(): This operator is a bracket operator used to declare and define the function.
[]: This operator is an array subscript operator
* : This operator is a pointer operator.
Identifier: It is the name of the pointer. The priority will always be assigned to this.
Data type: Data type is the type of the variable to which the pointer is intended to point. It also includes the modifier like signed int, long, etc).

How to read the pointer: int (*p)[10].

To read the pointer, we must see that () and [] have the equal precedence. Therefore, their associativity must be considered here. The associativity is left to right, so the priority goes to ().

Inside the bracket (), pointer operator * and pointer name (identifier) p have the same precedence. Therefore, their associativity must be considered here which is right to left, so the priority goes to p, and the second priority goes to *.

Assign the 3rd priority to [] since the data type has the last precedence. Therefore the pointer will look like following.

Char -> 4
* -> 2
p -> 1
[10] -> 3

The pointer will be read as p is a pointer to an array of integers of size 10.

Example

How to read the following pointer?

Int (*p)(int (*)[2], int (*)void))

Explanation

This pointer will be read as p is a pointer to such function which accepts the first parameter as the pointer to a one-dimensional array of integers of size two and the second parameter as the pointer to a function which parameter is void and return type is the integer.

Text Books:

1. Satinder Bal Gupta & Amit Singla, Fundamental of Computers and Programming in C, Shree Mahavir Book (Publishers), New Delhi

2. Ajay Mittal, Programming in C, ‘A Practical Approach’, Pearson Education.

3. Byron Gottfried, Schaum's Outline of Programming with C, McGraw-Hill

4. E. Balaguruswamy, Programming in ANSI C, Tata McGraw-Hill

5. YashavantKanetkar, Let Us C, BPB Publication.

Sign Up

Index

Notes

Highlighted

Underlined

Browse by Topics

Notes

Highlighted

Underlined