Question

How can I tell if a binary number is negative?

Currently I have the code below. It works fine converting to Binary. When converting to decimal, I need to know if the left most bit is 1 to tell if it is negative or not but I cannot seem to figure out how to do that.

Also, instead of making my Bin2 function print 1’s an 0’s, how can I make it return an integer? I didn’t want to store it in a string and then convert to int.

EDIT: I’m using 8 bit numbers.

int Bin2(int value, int Padding = 8)
{
    for (int I = Padding; I > 0; --I)
    {
        if (value & (1 << (I - 1)))
            std::cout<< '1';
        else
            std::cout<<'0';
    }

    return 0;
}

int Dec2(int Value)
{
    //bool Negative = (Value & 10000000);

    int Dec = 0;
    for (int I = 0; Value > 0; ++I)
    {
        if(Value % 10 == 1)
        {
            Dec += (1 << I);
        }
        Value /= 10;
    }

    //if (Negative) (Dec -= (1 << 8));

    return Dec;
}

int main()
{
    Bin2(25);
    std::cout<<"\n\n";
    std::cout<<Dec2(11001);
}

Answer 1

You are checking for negative value incorrectly. Do the following instead:

bool Negative = (value & 0x80000000); //It will work for 32-bit platforms only

Or may be just compare it with 0.

bool Negative = (value < 0);