Introduction - If you have any usage issues, please Google them yourself
Known a rational class Zrf_Ratio, the following form of operator overloading:
friend zrf_Ratio operator-(const zrf_Ratio &)
friend zrf_Ratio operator+ (const zrf_Ratio &, const zrf_Ratio &)
friend zrf_Ratio operator-(const zrf_Ratio &, const zrf_Ratio &)
friend zrf_Ratio operator* (const zrf_Ratio &, const zrf_Ratio &)
friend zrf_Ratio operator/(const zrf_Ratio &, const zrf_Ratio &)