Count Set Bits in an Integer

#include <stdio.h>

int countSetBits(unsigned int n) {
    // Write your code here
    unsigned int count =0;
    unsigned int pre = n;
    for(int i =0; i<=31;i++){
        (n &= (1<<i))!=0? count++ : NULL;
        n = pre;
    }
    return count;
}

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