Hello everybody. That is my code to show binary a decimal number. It's right when a>=0 but when a<0 that can't work, infinite loop. And I don't know what wrong in this code. Can you help me to solve? Thank so much!

void bi(int a)
{
        if(a==0)
            return;
        bi(a>>1);
        cout<<(a & (1));
}

//I have a nother code and it's right in both case. However I want to know what happen with this code. Sorry for my bad English