代码功能：将输入的中缀表达式转化为后缀表达式并进行一个值的求，支持括号。

思路：见代码。

#include <iostream>
#include <stack>
#include <string>
#include <vector>using namespace std;void showAndPush(vector<string> &expr, const string &s, char t = ' ') {expr.push_back(s);cout << s << t;
}bool isOper(const string &s) {return s.length() > 0 && (s[0] == '+' || s[0] == '-' || s[0] == '*' || s[0] == '/');
}int cal(int num, int num1, char oper) {switch (oper) {case '+': return num + num1;case '-': return num - num1;case '*': return num * num1;case '/': return num / num1;}
}void infixToSuffix(int &p, const string &text, vector<string> &expr) {stack<char> stk;int len = text.length();for (; p < len; ++p) {switch (text[p]) {case '+':case '-':while (!stk.empty() && (stk.top() == '*' || stk.top() == '/')) {cout << stk.top(); stk.pop();}stk.push(text[p]);break;case '*':case '/':stk.push(text[p]);break;case '(':infixToSuffix(++p, text, expr);break;case ')':while (!stk.empty()) {showAndPush(expr, string(1, stk.top()));stk.pop();}return;default:string num;while (isdigit(text[p])) {num.push_back(text[p]);++p;}--p;showAndPush(expr, num);}}while (!stk.empty()) {showAndPush(expr, string(1, stk.top()));stk.pop();}
}int calculate(const vector<string> &expr) {stack<int> num;for (auto &iter : expr) {if (isOper(iter)) {int t = num.top(); num.pop();int t1 = num.top(); num.pop();num.push(cal(t,t1,iter[0]));} else {num.push(stoi(iter));}}return num.top();
}void sln() {string text;cin >> text;vector<string> expr;int p = 0;infixToSuffix(p, text, expr);cout << endl;cout << calculate(expr) << endl;
}int main() {sln();return 0;
}

运行截图：

未处理除零、括号不匹配以及出现非法字符等错误。