//定义一个钱包类Wallet，有三个浮点数成员变量，rmb,jpy,usd分别代表人民币，日元和美元。重载运算符“-”，使之能用于浮点数（人民币）的减法运算。//参加运算的两个运算量可以都是类对象，也可以其中有一个是浮点数，顺序任意。//例如：w1 - w2，2 - w1 , w1 - 1.2均合法。#include<iostream>using namespace std;class Wallet{ public: Wallet(){rmb=0;jpy=0;usd=0;} friend Wallet operator-(Wallet &c1,Wallet &c2); friend Wallet operator-(Wallet &c1,float x); friend Wallet operator-(float x,Wallet &c1); void display(); void input(); private: float rmb,jpy,usd;};void Wallet::display(){cout<<"("<<rmb<<","<<jpy<<","<<usd<<")"<<endl;}void Wallet::input(){cin>>rmb>>jpy>>usd;}Wallet operator-(Wallet &c1,Wallet &c2){ Wallet c; c.rmb=c1.rmb-c2.rmb; c.jpy=c1.jpy-c2.jpy; c.usd=c1.usd-c2.usd; return c;}Wallet operator-(Wallet &c1,float x){ Wallet c; c.rmb=c1.rmb-x; c.jpy=c1.jpy; c.usd=c1.usd; return c;}Wallet operator-(float x,Wallet &c1){ Wallet c; c.rmb=x-c1.rmb; c.jpy=c1.jpy; c.usd=c1.usd; return c;}