Functions and pointers

Pointers are often used with functions in two ways.

Passing address to a function

If we want to modify the passed value of variable in function we must pass the address of variables to the function.

Example:

void display(int *ptr);

int string_length(char *str);

void swap(int *p1,int *p2);

C program using pointer as function argument:

#include<stdio.h>

change(int *ptr1,int *ptr2);

main()

{

int a=10,b=20;

printf("\nBefore Change a=%d b=%d",a,b);

change(&a,&b); //passing address to function as argument

14) printf("\nAfter Change a=%d b=%d\n",a,b);

}

change(int *ptr1,int *ptr2)//ptr1 points to a and ptr2 points to b

{ *ptr1=200;

*ptr2=300;

}

Before Change a=10 b=20

After Change a=200 b=300

Functions and pointers

C Program passing an array to a function :

#include<stdio.h>

main()

{ int a[10],n,i;

void display(int *x, int n);

printf("\n How many numbers:");

scanf("%d",&n);

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

scanf("%d",&a[i]);

printf("\n You entered \n");

display(a,n);

}

void display(int *ptr, int n)

{ int i;

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

printf("\t%d",*(ptr+i));

}

An array name is a pointer to the array. When we pass an array to a function, we are actually passing the base address of the array. This address can be stored in a pointer.

Function returning a pointer

Syntax : datatype * function_name(argument list);

Example: int *f1(int); char *f2 (int *,int*);

C program accepts the address of two integers variables and returns the address of the larger variable to main

#include<stdio.h>

void main()

{

int *larger(int*,int*); /* prototype*/

int n1,n2,*maxptr;

printf(“\nEnter two numbers:”);

scanf(“%d%d”,&n1,&n2);

maxptr=larger(&n1,&n2);

printf(“\n The larger number is %d:”,*maxptr);

}

int *larger(int *ptr1,int *ptr2)

{ if(*ptr1>*ptr2) return(ptr1);

else return(ptr2);

}

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