Bitwise Operators - Programming

Q1:

Which of the following statements are correct about the program?
#include<stdio.h>

int main()
{
    unsigned int num;
    int c=0;
    scanf('%u', &num);
    for(;num;num>>=1)
    {
        if(num & 1)
            c++;
    }
    printf('%d', c);
    return 0;
}

A It counts the number of bits that are ON (1) in the number num.

B It counts the number of bits that are OFF (0) in the number num.

C It sets all bits in the number num to 1

D Error

ANS:A - It counts the number of bits that are ON (1) in the number num.

If we give input 4, it will print 1.
Binary-4 == 00000000 00000100 ; Total number of bits = 1.

If we give input 3, it will print 2.
Binary-3 == 00000000 00000011 ; Total number of bits = 2.

If we give input 511, it will print 9.
Binary-511 == 00000001 11111111 ; Total number of bits = 9.