C | Pointer Basics | Question 17

Assume that float takes 4 bytes, predict the output of following program.

#include <stdio.h> 
  
int main() 
{ 
    float arr[5] = {12.5, 10.0, 13.5, 90.5, 0.5}; 
    float *ptr1 = &arr[0]; 
    float *ptr2 = ptr1 + 3; 
  
    printf("%f ", *ptr2); 
    printf("%d", ptr2 - ptr1); 
  
   return 0; 
} 

(A) 90.500000
3

(B) 90.500000
12
(C) 10.000000
12
(D) 0.500000
3

Answer: (A)

Explanation: When we add a value x to a pointer p, the value of the resultant expression is p + x*sizeof(*p) where sizeof(*p) means size of data type pointed by p. That is why ptr2 is incremented to point to arr[3] in the above code. Same rule applies for subtraction. Note that only integral values can be added or subtracted from a pointer. We can also subtract or compare two pointers of same type.

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