四则运算表达式求值——中缀表达式转后缀及计算

http://acm.zjnu.edu.cn/DataStruct/showproblem?problem_id=1004

题解：表达式计算 书上的模板

#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<stdlib.h>
#include<string>
#include<string.h>
#include<stack>
#include<iostream>
#include<list>
using namespace std;
const int maxn = 1e5 + 5;
stack<char>opr;
list<char> ans;
stack<int>num;

int cal(int aa, char o, int bb) {
    int a = aa;
    int b = bb;
    switch (o) {
    case'/':return a / b;
    case'*':return a*b;
    case'-':return a - b;
    case'+':return a + b;
    }
}
string mp[7];
//+-* / (  ) 
//01234 5
string ofrd = "+-*/()#";
int id(char c) {
    return ofrd.find(c);
}



char cmp(char a, char b) {
    return mp[id(a)][id(b)];
}
string ex;
int main() {
    mp[0] = mp[1] = ">><<<>>";
    mp[2] = mp[3] = ">>>><>>";
    mp[4] = "<<<<<=>";
    mp[5] = ">>>> >>";
    mp[6] = "<<<<< =";
    while (cin >> ex) {
        ex += '#';
        //ex = '#' + ex;
        while (!opr.empty())opr.pop();
        while (!num.empty())num.pop();
        ans.clear();
        int len = ex.length();
        int i = 0;
        opr.push('#');
        while (ex[i] != '#' || opr.top() != '#') {
            if (ex[i] >= '0'&&ex[i] <= '9') { num.push(ex[i] - '0'); ans.push_back(ex[i]); i++; }
            else {
                switch (cmp(opr.top(), ex[i])) {
                case'<':
                    opr.push(ex[i]);
                    i++;
                    break;
                case'=':
                    opr.pop();
                    i++;
                    break;
                case'>':
                    char c = opr.top();
                    opr.pop();
                    int  a = num.top(); num.pop();
                    int b = num.top(); num.pop();
                    ans.push_back(c);
                    a = cal(b, c, a);
                    
                    num.push(a);


                    break;
                }
            }
        }
        cout << ans.front(); ans.pop_front();
        for (auto t : ans)cout<< ' ' << t ;
        cout << endl;
        cout << num.top() << endl; num.pop();
    }

}