30. Count Set Bits in an Integer

#include <stdio.h>

#define IS_BIT_SET(reg, k) ((reg) & (1 << (k)))

int countSetBits(unsigned int n) {
    int num_set = 0;
    for(int i = 0; i < 32; i++)
    {
        num_set = (IS_BIT_SET(n, i)) ? num_set + 1 : num_set;
    }

    return num_set;
}

int main() {
    int n;
    scanf("%d", &n);
    printf("%d", countSetBits(n));
    return 0;
}