Bitwise right shift operator >> didn't work as intended

Question

I am writing a code to find the number of ones in binary representation of a number.

Here is the code:

int main(void)
{
    int n,tNum,count = 0;
    cin >> n;
    tNum = n;
    while(tNum > 0)
    {
        int i = 0;
        int bit = getBit(n,i);// get bit
        if (bit == 1)
        {
        count++;
        }
        tNum >> 1;
        i++;
    }
    cout << count << endl;
}

Above code gives an endless loop and tNum didn't change its value. I don't understand what I am doing wrong.

Answer 1

Bitwise right shift operator >> didn't worked as intended

The bitwise right shift operator >> is working as intended but you are not storing the result of >> operator anywhere. This expression

tNum >> 1;

will right shift the value of tNum by 1 but the result of this expression is unused.

Use >>= operator instead of >>. It should be:

        tNum >>= 1;

This is same as tNum = tNum >> 1.

Another problem in your code:

This

getBit(n,i);

will give the 0^th bit of n (as the i is initialised with 0 in every iteration) and which is going to be same for every iteration. Instead, you should get the 0^th bit of tNum as you are using shift operator on tNum below in your code. Also, you don't need i at all, just remove it. The statement should be:

int bit = getBit(tNum, 0);// get 0th bit

One more important point, the result of right shift >> of a negative number is implementation defined. May, you should use unsigned int type for n and tNum.

You can do:

int main (void)
{
    unsigned int n, tNum;
    int count = 0;

    cin >> n;
    tNum = n;
    while(tNum > 0)
    {
        int bit = getBit(tNum, 0);// get bit
        // You can also do
        // int bit = tNum & 1;

        if (bit == 1)
        {
            count++;
        }
        tNum >>= 1;
    }
    cout << count << endl;

    return 0;
}

Note: There is scope of improvement in the implementation of your code. I am leaving it up to you to identify those improvements and make respective changes in your code.