表达式求值

#pragma once
#include "stdafx.h"
#include "Stack.h"
//方法的声明实现的 分离写法 容易 报错，IDE还找不到错误的地方

//表达式求值
class Calculator {
private:
//Calculator's stack,运算存储区
Stack<double> s;
//7个方法
public:
//建立一个空计算器栈
Calculator(void) {}
//De建立一个空计算器栈
virtual ~Calculator() {}
//将一个double型操作数压入堆栈
void Enter(double operand) {
s.Push(operand);
}
//弹出2个操作数
void GetTwoOperands(double &operand1, double &operand2) {
if (s.IsEmpty()) {
cerr << "No operand to be pop !" << endl;
s.Clear();
exit(1);
}
operand1 = s.Pop();
if (s.IsEmpty) {
cerr << "No operand to be pop !" << endl;
s.Clear();
exit(1);
}
operand2 = s.Pop();
}
//操作符运算
void Compute(char op) {
double operand1, operand2, result;
GetTwoOperands(operand1, operand2);
switch (op) {
case '+': result = operand1 + operand2; break;
case '-': result = operand1 - operand2; break;
case '*': result = operand1 * operand2; break;
case '/': if (operand2 == 0) {
cerr << "Divided by 0 !" << endl;
s.Clear();
exit(1);
} else
result = operand1 / operand2; break;
default:
break;
}
s.Push(result);
}
//清空栈
void Clear() {
s.Clear();
}
//计算表达式的值
void Run() {
char op; //操作符
double operand; //操作数
cin >> op; //输入操作符
while (op != '=') {
switch (op) {
case'+':case'-':case'*':case'/':
Compute(op); break; //运算
default:cin.putback(op); //非操作符，回流
cin >> operand; //入操作数
Enter(operand); break; //入栈操作数
}
cin >> op; //输入操作符
}
cout << s.Pop() << endl;//最后出栈
Clear();//清空栈
}
};//!_class Calculator