Declaring and Initializing Pointer Variables - C Pointer

C examples for Pointer:Pointer Variable

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Introduction

Place the indirection operator * in front of the variable name to declare a pointer.

Pointer variables must be declared before they can be used:

Demo Code

#include <stdio.h> 
int main()/*from ww  w .  jav  a  2 s .  c o  m*/
{ 

    int x = 0; 
    
    int iAge = 30; 
    
    int *ptrAge; 
}

To indirectly reference a value through a pointer, you must assign an address to the pointer. 

ptrAge = &iAge;

In this statement, I assign the memory address of the iAge variable to the pointer variable ptrAge.

The unary operator & is referred to as the "address of" operator.

You can assign the contents of what the pointer variable points to-a non-pointer data value. 

x = *ptrAge;

The variable x will now contain the integer value of what ptrAge points to-in this case the integer value 30.

Pointer variables should be initialized with another variable's memory address, with 0, or with the keyword NULL.

The next code block demonstrates a few valid pointer initializations.

Demo Code

#include <stdio.h> 
int main()/*  w  w w .  j  a  v  a 2s  .co  m*/
{ 
    int *ptr1; 
    int *ptr2; 
    int *ptr3; 
    
    int x = 5; 
       
    ptr1 = &x; 
    ptr2 = 0; 
    ptr3 = NULL; 
    
    printf("point variable defined.");
}

Result

Assign address to pointer 

#include <stdio.h> 
int main()
{ 
   int x = 5; 
   int *iPtr; 

   iPtr = 5; //this is wrong 
   iPtr = x; //this is also wrong  
 
   iPtr = &x;  //iPtr is assigned the address of x 
   *iPtr = 7;  //the value of x is indirectly changed to 7 
   
   printf("");
}

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