bitwise or and assignment

Question

#include <stdio.h>

#define NUMVALS 6
#define SIZE 5
#define MAX 31

int main () {

   int vals = 0;

   short curVal, idx = 0;


   for(; idx < NUMVALS; ++idx) {
      scanf("%d", &curVal);

      vals = (vals << SIZE) | curVal;
   }

   printf("%d", vals | curVal);

   return 0;
}

This is some code I am working on. It is supposed to store 6 integers each in the range from 0 to 31, so each gets a space of 5 bits. For some reason it is not working. When I make the assignment to vals in the loop, it seems to only be storing the current value read in into vals. Do you see what might be going wrong?

Answer 1

A halfway decent compiler will tell you:

warning: format ‘%d’ expects argument of type ‘int *’, but argument 2 has type ‘short int *’
     scanf("%d", &curVal);

You need to use %hd to scan a short, or (in this case better) change your variable to int.

If you're using GCC, add -Wall -Wextra -Werror to your compilation command. It would have caught this for you.