pointer

Q.Write a "C" Program using function to swap to number

#include<stdio.h>

#include<conio.h>

/* function prototype */

void swap(int* ,int*);

void main()

{

     int a,b;

     clrscr();

       printf("\nEnter the value of a and b:");

     scanf("%d %d",&a,&b);

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

     swap(&a,&b); /*function call */

     printf("\nAfter Swap , a = %d , b=%d",a,b);

     getch();

}

/*function definition */

void swap(int *a,int *b)

{

     int c;

     c=*a;

     *a=*b;

     *b=c;

}

    

Find the output of the following program :

(i)

     #include<stdio.h>    

     #include<conio.h>

     main()

     {

          int i=4,j=5;

          junk(i,&j);

          printf("\n %d %d",i,j);

     }

     junk(int i,int *j)

     {

          i=i*i;

          *j=*j**j;

     }

i=4

j=25

             

#include<stdio.h>

#include<conio.h>

void main()

{

     int i=16;

     float f=3.14;

     char c='A';

     char *cc;

     cc=&c;

     printf("\n cc = %u  , *cc= %c",cc,*cc);

     cc=&i;

     printf("\n cc = %u  , *cc= %c",cc,*cc);

     cc=&f;

     printf("\n cc = %u  , *cc= %c",cc,*cc);

     getch();

}

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Reference Variables :

The reference variable will store the reference of the variable. The general form of declaring the reference variable is ,

     datatype & referencevariablename=variablename;

e.g.

     int a=10;

     int &b=a;

     Now, b will be the reference variable and it will reference to a.

The reference variable is prefixed by an ampersand sign at the time of its declaration.     As , the pointer variable will store the address of the variable , the reference variable will store    the     refernce of the variable. That is , it will reference to the same location to which the variable    is referencing to.

     In case of pointers ,

          int a=10;

          int *b;

          b=&a;

                   

     In case of reference variable,

          int a=10;

          int &b=a;

              

          So , if we make any change in b , the change will get reflected in a and vice versa.

In c++, the reference variable can be used in three different ways ,

     (a) Independent Reference variable

     (b) Passing references to the functions

     (c) Returning references from the function.

     (a) Independent References Variables :

          Consider the following programs ,

     #include<iostream.h>

     #include<conio.h>

     void main()

     {

          int a=10;

          int &b=a;

cout<<endl<<"a= " << a <<" b="<<b;

          a=a+2;

          cout<<endl<<"a= " << a <<" b="<<b;

          b=b-1;

cout<<endl<<"a= " << a <<" b="<<b;

          int c=50;

          b=c;

cout<<endl<<"a= " << a <<" b="<<b<<"c="<<c;

          b=b+5;

          cout<<endl<<"a= " << a <<" b="<<b<<"c="<<c;

          getch();

}

output :

a=10 b=10

a=12 b=12

a=11 b=11

a=50 b=50 c=50

a=55 b=55 c=50

(b) Passing references to the function

Consider the following program ,

#include<iostream.h>

#include<conio.h>

/*function prototype*/

void swap(int & , int &);

void main()

{

     int a,b;

     clrscr();

cout<<endl<<"Enter the value of a and b:";

     cin>>a>>b;

cout<<endl<<"Before Swap a="<<a<<" b= "<<b;

swap(a,b); /*function call*/

cout<<endl<<"After Swap a="<<a<<" b="<<b;

getch();

}

/*function definition*/

void swap(int & x , int &y)

{

     int z;

     z=x;

     x=y;

     y=z;

}

Now , we have used the reference variables in the formal arguments ,so they will reference to the actual arguments , so the changes which we make in the formal arguments will also get reflected in the actual arguments.This is known as Call By Reference

(c) Returning References from the functions .

     Consider the following program ,

     #include<iosteam.h>

     #include<conio.h>

     /*fucntion prototypr*/

     char & func(int);

     /*global declaration */

          char s[ ] = "Hello World";

     void main()

     {

          func(5)='*'; /*function call*/

    

          cout<<endl<<s;

    

          getch();

     }

     /*function defintion */

     char & func(int pos)

     {

          return s[pos];

     }

output : Hello*World