Question

What is the output of the following program?
# include <stdio.h>
int main ( )
{
int x = 5;
int * const ptr = &x;
++(*ptr)
printf("%d", x);
return 0;
}

• A. 6
• B. 5
• C. Runtime Error
• D. Compiler Error

Answer 1

The correct option is A 6

See following declarations to know the difference between constant pointer and a pointer to a constant.
int* constptr $\to$ ptr is constant pointer. You can change the value at the location pointed by pointer p, but you cannot change p to point to other location.

int const * ptr $\to$ ptr is a pointer to a constant. You can change ptr to point other variable. But you cannot change the value pointed by ptr.
Therefore above program works well because we have a constant pointer and we are not changing ptr to point to any other location.
We are only incrementing value pointed by ptr.