Pointer Arithmetic

In C pointer holds address of a value, so there can be arithmetic operations on the pointer variable. Following arithmetic operations are possible on pointer in C language:
  • Increment
  • Decrement
  • Addition
  • Subtraction
  • Comparison
    •

    Incrementing Pointer

    Incrementing a pointer is used in array because it is contiguous memory location. Moreover, we know the value of next location.
    Increment operation depends on the data type of the pointer variable. The formula of incrementing pointer is given:
    new_address= current_address + i * size_of(data type)
  • 32 bit
    •  For 32 bit int variable, it will increment to 4 byte.
  • 64 bit
    •  For 64 bit int variable, it will increment to 8 byte.
    see the example of incrementing pointer variable on 64 bit OS.
    #include <stdio.h>  
void main(){          
int number = 40;      
int *p;   //pointer to int    
p=&number;  //stores the address of number variable      
printf("Address of p variable is %u \n",p);      
p=p+1;     
printf("After increment: Address of p variable is %u \n",p);      
}    
Output
Address of p variable is 32104
After increment: Address of p variable is 32112

    Decrementing Pointer

    new_address= current_address - i * size_of(data type)
  • 32 bit
    •  For 32 bit int variable, it will decrement to 4 byte.
  • 64 bit
    •  For 64 bit int variable, it will decrement to 8 byte.
    see the example of decrementing pointer variable on 64 bit OS.
    #include <stdio.h>  
void main(){          
int number=50;      
int *p;   //pointer to int    
p = &number;   //stores the address of number variable      
printf("Address of p variable is %u \n",p);      
p = p-1;     
printf("After decrement: Address of p variable is %u \n",p);      
}    
Output
Address of p variable is 321100 
After decrement: Address of p variable is 32192

    Pointer Addition

    We can add a value to the pointer variable. The formula of adding value to pointer is given:
    new_address= current_address + (number * size_of(data type))
  • 32 bit
    •  For 32 bit int variable, it will add 4 * number.
  • 64 bit
    •  For 64 bit int variable, it will add 8 * number.
    see the example of adding value to pointer variable on 64 bit OS.
    #include <stdio.h>  
#include           
void main()  {          
int number = 40;      
int *p;  //pointer to int    
p=&number;//stores the address of number variable      
printf("Address of p variable is %u \n",p);      
p=p+2;   //adding 2 to pointer variable  
printf("After adding 2: Address of p variable is %u \n",p);      
  }    
Output:
Address of p variable is 321100 
After adding 2: Address of p variable is 321116

    Pointer Subtraction

    Like pointer addition, we can subtract a value from the pointer variable. The formula of subtracting value from pointer variable is given :
    new_address= current_address - (number * size_of(data type))
  • 32 bit
    •  For 32 bit int variable, it will subtract 4 * number.
  • 64 bit
    •  For 64 bit int variable, it will subtract 8 * number.
    see the example of subtracting value to pointer variable on 64 bit OS.
    #include <stdio.h>  
#include           
void main()  {                   
int number = 50;      
int *p;   //pointer to int    
p=&number;  //stores the address of number variable      
printf("Address of p variable is %u \n",p);      
p=p-2;    //subtracting 2 from pointer variable  
printf("After subtracting 2: Address of p variable is %u \n",p);      
  }    
Output:
Address of p variable is 321100 
After subtracting 2: Address of p variable is 321084