PPS 6.6.FUNCTION INTRODUCTION & WRITING FUNCTIONS, SCOPE OF VARIABLES FUNCTIONS

PPS
Unit – 6
Function
6.1 Introduction & Writing Functions
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;

}
6.2 Scope Of Variables Functions (Including Using Built In Libraries)
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
1. 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.
6.3 Parameter Passing In Functions, Call By Value
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 = %dn", a, b );
swap( a, b );
printf("After: Value of a = %d and value of b = %dn", 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) = %dn", 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;

swap(&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) = %dn", *p1, *p2 );
}
Output :
Value of a (p1) = 20 and value of b(p2) = 10
Note: In the above example the values of “a” and “b” are changes after calling swap
function.
6.4 Passing Arrays To Functions: Idea Of Call By Reference
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
1. #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
Value of tenth element of the array is
printed

%d",a[9]);
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;
swap( 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) = %dn", p1, p2 );
}
Output :
Value of a (p1) = 20 and value of b (p2) = 10
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

PPS 6.6.FUNCTION INTRODUCTION & WRITING FUNCTIONS, SCOPE OF VARIABLES FUNCTIONS

PPS 6.6.FUNCTION INTRODUCTION & WRITING FUNCTIONS, SCOPE OF VARIABLES FUNCTIONS

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PPS 6.6.FUNCTION INTRODUCTION & WRITING FUNCTIONS, SCOPE OF VARIABLES FUNCTIONS