请给出代码c++

以下是一个简单的 C++ 实现，实现了基本要求中的功能，但没有添加选做内容。代码中使用了两个栈来实现括号匹配和逆波兰表达式的转换。

#include <iostream>
#include <stack>
#include <string>
#include <cctype>
#include <cstring>

using namespace std;

// 判断运算符的优先级
int getPriority(char c) {
    switch (c) {
        case '+':
        case '-':
            return 1;
        case '*':
        case '/':
            return 2;
        case '^':
            return 3;
        default:
            return 0;
    }
}

// 判断运算符的结合性
bool isLeftAssociative(char c) {
    return (c != '^');
}

// 将中缀表达式转换为逆波兰表达式
string infixToPostfix(string infix) {
    stack<char> opStack;
    string postfix;
    for (int i = 0; i < infix.size(); i++) {
        if (isdigit(infix[i]) || infix[i] == '.') {
            postfix += infix[i];
            while (isdigit(infix[i+1]) || infix[i+1] == '.') {
                i++;
                postfix += infix[i];
            }
            postfix += ' ';
        }
        else if (infix[i] == '(') {
            opStack.push(infix[i]);
        }
        else if (infix[i] == ')') {
            while (!opStack.empty() && opStack.top() != '(') {
                postfix += opStack.top();
                postfix += ' ';
                opStack.pop();
            }
            if (!opStack.empty() && opStack.top() == '(') {
                opStack.pop();
            }
            else {
                return "Error: Mismatched parentheses\n";
            }
        }
        else if (infix[i] == '+' || infix[i] == '-' || infix[i] == '*' || infix[i] == '/' || infix[i] == '^') {
            while (!opStack.empty() && opStack.top() != '(' && ((isLeftAssociative(infix[i]) && getPriority(infix[i]) <= getPriority(opStack.top())) || (!isLeftAssociative(infix[i]) && getPriority(infix[i]) < getPriority(opStack.top())))) {
                postfix += opStack.top();
                postfix += ' ';
                opStack.pop();
            }
            opStack.push(infix[i]);
        }
        else {
            return "Error: Invalid character\n";
        }
    }
    while (!opStack.empty()) {
        if (opStack.top() == '(' || opStack.top() == ')') {
            return "Error: Mismatched parentheses\n";
        }
        postfix += opStack.top();
        postfix += ' ';
        opStack.pop();
    }
    return postfix;
}

// 对逆波兰表达式求值
double evaluatePostfix(string postfix) {
    stack<double> numStack;
    char* token = strtok(&postfix[0], " ");
    while (token != NULL) {
        if (isdigit(token[0]) || (token[0] == '-' && isdigit(token[1]))) {
            numStack.push(atof(token));
        }
        else if (token[0] == '+' || token[0] == '-' || token[0] == '*' || token[0] == '/' || token[0] == '^') {
            if (numStack.size() < 2) {
                return NAN;
            }
            double b = numStack.top();
            numStack.pop();
            double a = numStack.top();
            numStack.pop();
            switch (token[0]) {
                case '+':
                    numStack.push(a + b);
                    break;
                case '-':
                    numStack.push(a - b);
                    break;
                case '*':
                    numStack.push(a * b);
                    break;
                case '/':
                    numStack.push(a / b);
                    break;
                case '^':
                    numStack.push(pow(a, b));
                    break;
            }
        }
        else {
            return NAN;
        }
        token = strtok(NULL, " ");
    }
    if (numStack.size() == 1) {
        return numStack.top();
    }
    else {
        return NAN;
    }
}

// 判断中缀表达式中的括号是否匹配
bool isParenthesesMatched(string infix) {
    stack<char> parenStack;
    for (int i = 0; i < infix.size(); i++) {
        if (infix[i] == '(') {
            parenStack.push(infix[i]);
        }
        else if (infix[i] == ')') {
            if (parenStack.empty() || parenStack.top() != '(') {
                return false;
            }
            else {
                parenStack.pop();
            }
        }
    }
    return parenStack.empty();
}

int main() {
    while (true) {
        cout << "Calculator\n\n";
        cout << "Select an option:\n";
        cout << "1. Evaluate expression\n";
        cout << "2. Exit\n\n";
        cout << "Option: ";
        int option;
        cin >> option;
        if (option == 1) {
            cout << "Enter an expression: ";
            string infix;
            cin >> infix;
            if (isParenthesesMatched(infix)) {
                string postfix = infixToPostfix(infix);
                if (postfix.substr(0, 6) == "Error:") {
                    cout << postfix << endl;
                }
                else {
                    double result = evaluatePostfix(postfix);
                    if (isnan(result)) {
                        cout << "Error: Invalid expression\n";
                    }
                    else {
                        cout << "Result: " << result << endl;
                    }
                }
            }
            else {
                cout << "Error: Mismatched parentheses\n";
            }
        }
        else if (option == 2) {
            break;
        }
        else {
            cout << "Invalid option\n";
        }
        cout << endl;
    }
    return 0;
}