A riddle (in C)

Question

A friend gave me a riddle:

#include<stdio.h>

#define TOTAL_ELEMENTS ((sizeof(array) / sizeof(array[0])))
  int array[] = {23,34,12,17,204,99,16};

  int main()
  {
      int d;
      for(d=-1;d <= (TOTAL_ELEMENTS-2);d++)
          printf("%d\n",array[d+1]);
      getchar();
      return 0;
  }

The above code is supposed to print all the array elements, what is the problem in the code (the output is nothing)? I think the loop doesn't iterate even once?

I found out that the following code does work:

#include<stdio.h>



#define TOTAL_ELEMENTS ((sizeof(array) / sizeof(array[0])))
  int array[] = {23,34,12,17,204,99,16};

  int main()
  {
      int d;
      int x = (TOTAL_ELEMENTS-2);
      for(d=-1;d <= x;d++)
          printf("%d\n",array[d+1]);
      getchar();
      return 0;
  }

I have a theory that it's something to do with the macro, but I can't put my finger on the problem.

Answer 1

The problem is that (TOTAL_ELEMENTS-2) is an unsigned value. When you make the comparison d <= (TOTAL_ELEMENTS-2), both values are converted to unsigned values, and the result is false.

In your second example, x is signed so there is no problem.