一个C++分数计算器的程序，通分函数有错误，求指点，怎么改？

这是两个函数，上面约分函数应该是正确的，
求怎样调用约分函数写通分函数

void Grade::Reduction()//约分
{
    int a, b, CommonDivisor, Remainder;//公约数,余数
    a = abs(numerator);//分子取绝对值
    b = abs(denominator);//分母取绝对值
    {
        if (a > b)
        {
            Remainder = a % b;
            while (Remainder != 0)
            {
                int t;
                t = Remainder;
                a = b;
                b = t;
                Remainder = a % b;
            }
            CommonDivisor = b;
        }
        if (a == b)
        {
            CommonDivisor = a;
        }
        if (a < b)
        {
            Remainder = b % a;
            while (Remainder != 0)
            {
                int t;
                t = Remainder;
                b = a;
                a = t;
                Remainder = b % a;
            }
            CommonDivisor = a;
        }
    }//最大公约
    numerator /= CommonDivisor;//约分后分子
    denominator /= CommonDivisor;//约分后分母
}

void Grade::ToCommond(Grade &grade)  //通分
{
int temp;
    Reduction();
    grade.Reduction();
    numerator *= grade.denominator;
    grade.numerator *= denominator;

//////////后面不会写了