[C++]求表达式的逆波兰式

// ReversePolish2.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include 
#include 
#include 
#include 
using std::cout;
using std::cin;
using std::endl;
using std::stack;
using std::string;

int priority(char c) {
    switch (c)
    {
    case '+':
        return 1;
    case '-':
        return 1;
    case '*':
        return 2;
    case '/':
        return 2;
    default:
        return 0;
    }
}

template<class T> string printStack(stack stack) {
    string result = "";
    while (!stack.empty())
    {
        result = stack.top()+result;
        stack.pop();
    }
    return result;
}

string reversePolish(string inputStr) {
    stack<char> polish;
    stack<char> opStack;
    bool lastIsNum = false;
    for (int i = 0; i < inputStr.length(); i++) {
        char curChar = inputStr.at(i);
        //如果是数字
        if (curChar >= '0' && curChar <= '9') {
            if (!lastIsNum)
                polish.push(' ');
            polish.push(curChar);
            lastIsNum = true;
            continue;
        }
        //否则为操作符
        else if (curChar == '(') {
            opStack.push(curChar);
        }
        else if (!opStack.empty() && curChar == ')') {
            while (opStack.top() != '(')
            {
                polish.push(opStack.top());
                opStack.pop();
            }
            opStack.pop();
        }
        else {
            if (!opStack.empty() && opStack.top() == '(') {
                opStack.push(curChar);
            }
            else {
                if (!opStack.empty() && priority(curChar) > priority(opStack.top())) {
                    opStack.push(curChar);
                }
                else {
                    while (!opStack.empty())
                    {
                        if (opStack.top() == '(')
                            break;
                        if (priority(curChar) <= priority(opStack.top())) {
                            polish.push(opStack.top());
                            opStack.pop();
                        }
                        else {
                            break;
                        }
                    }
                    opStack.push(curChar);
                }
            }
        }
        lastIsNum = false;
    }

    while (!opStack.empty()) {
        polish.push(opStack.top());
        opStack.pop();
    }
    return printStack(polish);
}

int main()
{
    string str;
    cout << "请输入表达式: ";
    cin>>str;
    string result = reversePolish(str);
    cout << result<< endl;
    system("pause");
    return 0;
}

数字之间以空格隔开以便于下一步计算表达式的值