C | Data Types | Question 1

Predict the output of following program. Assume that the numbers are stored in 2’s complement form.

#include<stdio.h>
int  main()
{
   unsigned int x = -1;
   int y = ~0;
   if (x == y)
      printf("same");
   else
      printf("not same");
   return 0;
}

(A) same
(B) not same


Answer: (A)

Explanation: -1 and ~0 essentially have same bit pattern, hence x and y must be same. In the comparison, y is promoted to unsigned and compared against x (See this for promotion rules). The result is “same”. However, when interpreted as signed and unsigned their numerical values will differ. x is MAXUNIT and y is -1. Since we have %u for y also, the output will be MAXUNIT and MAXUNIT.


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