30. Count Set Bits in an Integer

#include <stdio.h>

int countSetBits(unsigned int n) {
    unsigned int count = 0;
    while(n) {
        count += n & 1;
        n >>= 1;
    }
    return count;
}

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

In the countSetBits function, we define an unsigned int count which counts the number of set bits in the given integer. 

We then do bitwise AND'ing of each bit in n while iterating through it. 
if n & 1 == 1, we get count + 1

We then right shift n