pointer examples

 

   

1)   Meaning of following simple pointer declaration and definition:

 

int a=5;

int * ptr;

ptr=&a;

Explanation:

About variable a:

1. Name of variable: a

2. Value of variable which it keeps: 5

3. Address where it has stored in memory: 1025 (assume)

About variable ptr:

4. Name of variable: ptr

5. Value of variable which it keeps: 1025

6. Address where it has stored in memory: 5000 (assume)

Pictorial representation:

 

 

 

 

 

Note: A variable where it will be stored in memory is decided by operating system. We cannot guess at which location a particular variable will be stored in memory.

(2) Meaning of following pointer declaration and definition:

int a=50;

int *ptr1;

int **ptr2;

ptr1=&a;

ptr2=&pt1;

 

Explanation:

About variable a:

1. Name of variable: a

2. Value of variable which it keeps: 50

3. Address where it has stored in memory: 5000 (assume)

About variable ptr1:

4. Name of variable: ptr1

5. Value of variable which it keeps: 5000

6. Address where it has stored in memory: 9000 (assume)

About variable ptr2:

7. Name of variable: ptr2

8. Value of variable which it keeps: 9000

9. Address where it has stored in memory: 9555 (assume)

Pictorial representation of above pointer declaration and definition:

 

 

Note:

 

‘*‘is known as indirection operator which gives content of any variable.

& is known as reference operator which gives address where variable has stored in memory.

 

Cancellation rule of above two operators:

 

* and & operators always cancel to each other i.e.

*&p=p

But it is not right to write:

&*p=p

Simple example:

 

What will be output of following c program?

#include<stdio.h>

int main(){

int x=25;

int *ptr=&x; //statement one

int **temp=&ptr; //statement two

printf(“%d %d %d”.x.*ptr,**temp);
return 0;

}

 

Output: 25 25 25

Explanation:

As we know value of variable x is 25.

 

*ptr= *(&x) //from statement one

=*&x

=x //using cancellation rule

=25

**temp= **(&ptr)=*(*&ptr)=*ptr=*(&x)=*&x=x=25

Example :-

#include<stdio.h>

main()

{

int x=10,*ptr;

clrscr();

ptr = &x;//(address of the variable)

*ptr = x;//(value of the variable)

printf("address of x=%d\n",ptr);

(or)

printf("address of x=%d\n",&x);

printf("value of x=%d\n",*ptr);

(or)

printf("value of x=%d\n",x);

getch();

}

output :-

address of x= -12

address of x= -12

value of x= 10

value of x= 10