Unit – 6
Function
Similar to other languages C language also provides the facility of function. Function is the block of code which is used to perform a specific task. In c language the complete program is composed of function.
Functions are useful to divide c programs into smaller modules. Programmer can invoked these modules anywhere inside c program for any number of times.
Functions are used to increase readability of the code. Size of program can be reduce by using functions. By using function, programmer can divide complex tasks into smaller manageable tasks and test them independently before using them together.
Functions of C language are defined with the type of function. The type of functions indicates the data type of value which will return by function. In order to use function in the program, initially programmer have to inform compiler about the function. This is also called as defining a function.
In C programme all the function definition present outside the main function. All function need to be declared and defined before use. Function declaration requires function name, argument list, and return type.
Return Type Function name (Argument list)
{
Statement 1;
Statement 2;
…………...
Statement n;
}
1. Library Functions
A function which is predefined in c language is called library function. Library function is also called as built in function of C language. The definition of library function is stored in respective header file. Library functions are used to perform dedicated operation like taking input from user, displaying output, string handling operation, etc. Library functions are readily available and programmer can directly use it without writing any extra code. For example, printf () and scanf () are library function and their definition is stored in stdio header file.
2. User Defined Functions
User define function is the block of code written by programmer to perform a particular task. As compiler doesn’t have any idea about the user define function so programmer has to define and declare these functions inside the program body. Programmer can define these function outside the main function but declaration of user define function should present in main function only. Whenever compiler executes function call (function declaration) then compiler shift the flow of program execution to the definition part of user define function.
Example
#include <stdio.h>
#include<conio.h>
int add (int x, int y)
{
int sum;
sum = x + y;
return (sum);
}
main ()
{
inta,b,c;
a = 15;
b = 25;
c = add(a,b);
printf ("\n Addition is %d ", c);
}
Output:
Addition is 40
There are two ways to pass the parameters to the function
- Parameter Passing by value
In this mechanism, the value of the parameter is passed while calling the function.
2. Parameter Passing by reference
In this mechanism, the address of the parameter is passed while calling the function.
Parameter Passing by Value
This is the default way of passing the parameters to the function. This is achieved by passing the copy of data to the function. This mechanism is also called as call by value. In case of parameter passing by value, the changes made to the formal arguments in the called function have no effect on the values of actual arguments in the calling function.
This mechanism is used when programmer don't want to change the value of passed parameters. When parameters are passed by value then functions in C create copies of the passed in variables and do required processing on these copied variables.
Pass-by-value is implemented by actual data transfer so additional storage is required to maintain the copies of passed parameters.
Example:
#include <stdio.h>
#include<conio.h>
/* function declaration goes here.*/
void swap( int p1, int p2 );
int main()
{
int a = 10;
int b = 20;
printf("Before: Value of a = %d and value of b = %d\n", a, b );
swap( a, b );
printf("After: Value of a = %d and value of b = %d\n", a, b );
getch();
}
void swap( int p1, int p2 )
{
int t;
t = p2;
p2 = p1;
p1 = t;
printf("Value of a (p1) = %d and value of b(p2) = %d\n", p1, p2 );
}
Output :
Before: Value of a = 10 and value of b = 20
Value of a (p1) = 20 and value of b (p2) = 10
After: Value of a = 10 and value of b = 20
Note: In the above example the values of “a” and “b” remain unchanged before calling swap function and after calling swap function.
Parameter Passing by Reference
This mechanism is used when programmer want a function to do the changes in passed parameters and reflect those changes back to the calling function. This mechanism is also called as call by reference. This is achieved by passing the address of variable to the function and function body can directly work over the addresses. Advantage of pass by reference is efficiency in both time and space. Whereas disadvantages are access to formal parameters is slow and inadvertent and erroneous changes may be made to the actual parameter.
Example:
#include <stdio.h>
#include<conio.h>
void swap( int *p1, int *p2 );
int main()
{
int a = 10;
int b = 20;
printf("Before: Value of a = %d and value of b = %d\n", a, b );
swap(&a, &b );
printf("After: Value of a = %d and value of b = %d\n", a, b );
}
void swap( int *p1, int *p2 )
{
int t;
t = *p2;
*p2 = *p1;
*p1 = t;
printf("Value of a (p1) = %d and value of b(p2) = %d\n", *p1, *p2 );
}
Output :
Before: Value of a = 10 and value of b = 20
Value of a (p1) = 20 and value of b(p2) = 10
After: Value of a = 20 and value of b = 10
Note: In the above example the values of “a” and “b” are changes after calling swap function.
Array is a data structure which stores the collection of similar types of element in consecutive memory locations. Indexing of array always start with ‘0’ where as non-graphical variable ‘\0’ indicates the end of array. Syntax for declaring array is
data type array name[Maximum size];
- Data types are used to define type of element in an array. Data types are also useful in finding the size of total memory locations allocated for the array.
- All the rules of defining name of variable are also applicable for the array name.
- Maximum size indicates the total number of maximum elements that array can hold.
- Total memory allocated for the array is equal to the memory required to store one element of the array multiply by the total element in the array.
- In array, memory allocation is done at the time of declaration of an array.
Example:
Sr. No. | Instructions | Description |
#include<stdio.h> | Header file included | |
2. | #include<conio.h> | Header file included |
3. | void main() | Execution of program begins |
4. | { | Memory is allocated for variable i,n and array a |
5. | inti,n,a[10]; | |
6. | clrscr(); | Clear the output of previous screen |
7. | printf("enter a number"); | Print “enter a number” |
8. | scanf("%d",&n); | Input value is stored at the addres of variable n |
9. | for(i=0;i<=10;i++) | For loop started from value of i=0 to i=10 |
10. | { | Compound statement(scope of for loop starts) |
11. | a[i]=n*i; | Result of multiplication of n and I is stored at the ith location of array ieasi=0 so it is stores at first location. |
12. | printf("\n %d",a[i]); | Value of ith location of the array is printed |
13. | } | Compound statement(scope of for loop ends) |
14. | printf("\n first element in array is %d",a[0]); | Value of first element of the array is printed |
15. | printf("\n fifth element in array is %d",a[4]); | Value of fifth element of the array is printed |
16. | printf("\n tenth element in array is %d",a[9]); | Value of tenth element of the array is printed |
17. | getch(); | Used to hold the output screen |
18. | } | Indicates end of scope of main function |
This is the default way of passing the parameters to the function. This is achieved by passing the copy of data to the function. This mechanism is also called as call by value. In case of parameter passing by value, the changes made to the formal arguments in the called function have no effect on the values of actual arguments in the calling function.
This mechanism is used when programmer don't want to change the value of passed parameters. When parameters are passed by value then functions in C create copies of the passed in variables and do required processing on these copied variables.
Pass-by-value is implemented by actual data transfer so additional storage is required to maintain the copies of passed parameters.
Example:
#include <stdio.h>
#include<conio.h>
/* function declaration goes here.*/
void swap( int p1, int p2 );
int main()
{
int a = 10;
int b = 20;
printf("Before: Value of a = %d and value of b = %d\n", a, b );
swap( a, b );
printf("After: Value of a = %d and value of b = %d\n", a, b );
getch();
}
void swap( int p1, int p2 )
{
int t;
t = p2;
p2 = p1;
p1 = t;
printf("Value of a (p1) = %d and value of b(p2) = %d\n", p1, p2 );
}
Output :
Before: Value of a = 10 and value of b = 20
Value of a (p1) = 20 and value of b (p2) = 10
After: Value of a = 10 and value of b = 20
Note: In the above example the values of “a” and “b” remain unchanged before calling swap function and after calling swap function.
Reference
- Brian W. Kernighan And Dennis M. Ritchie, The C Programming Language, Prentice Hall Of India
- YashwantKanetkar, Let Us C, Bpb Publication
