SillyMaths.cpp

// sub, mul, and div using only the "+" operator...

int negate(int a)
{
    int i = a < 0 ? 1 : -1;
    int ret = 0;
    for(; a != 0; a += i)
        ret += i;

    return ret;
}

int sub(int a, int b)
{
    return a + negate(b);
}

int mul(int a, int b)
{
    if(a == 0 || b == 0)
        return 0;

    b = a < 0 ? negate(b) : b;
    a = a < 0 ? negate(a) : a;

    int temp = 0;
    for(; a != 0; a += -1)
        temp += b;
    
    return temp;
}

int div(int a, int b)
{
    if(b == 0 || a == 0)
        return 0;

    int i = ((a < 0 && b < 0) || (a > 0) && (b > 0)) ? 1 : -1;
    b = b < 0 ? negate(b) : b;
    a = a < 0 ? negate(a) : a;

    int counter = 0;
    int ret = 0;
    for(; a != 0; a += -1)
    {
        counter++;
        if(counter == b)
        {
            ret += i;
            counter = 0;
        }
    }

    return ret;
}