只用中缀形式输出完整代码实现简单计算器

以下是一个简单的计算器实现，支持加、减、乘、除、括号和小数点：

#include <iostream>
#include <stack>
#include <string>
#include <sstream>
using namespace std;

bool isOperator(char c) {
    return c == '+' || c == '-' || c == '*' || c == '/';
}

bool isLeftParenthesis(char c) {
    return c == '(';
}

bool isRightParenthesis(char c) {
    return c == ')';
}

int precedence(char c) {
    if (c == '+' || c == '-') {
        return 1;
    } else if (c == '*' || c == '/') {
        return 2;
    } else {
        return 0;
    }
}

double evaluate(double a, double b, char op) {
    if (op == '+') {
        return a + b;
    } else if (op == '-') {
        return a - b;
    } else if (op == '*') {
        return a * b;
    } else if (op == '/') {
        return a / b;
    } else {
        return 0;
    }
}

double evaluatePostfix(string expr) {
    stack<double> s;
    for (int i = 0; i < expr.length(); i++) {
        char c = expr[i];
        if (isdigit(c)) {
            double num = 0;
            while (isdigit(c) || c == '.') {
                num = num * 10 + (c - '0');
                i++;
                c = expr[i];
            }
            i--;
            s.push(num);
        } else if (isOperator(c)) {
            double b = s.top();
            s.pop();
            double a = s.top();
            s.pop();
            double result = evaluate(a, b, c);
            s.push(result);
        }
    }
    return s.top();
}

string infixToPostfix(string expr) {
    stack<char> s;
    stringstream result;
    for (int i = 0; i < expr.length(); i++) {
        char c = expr[i];
        if (isdigit(c)) {
            while (isdigit(c) || c == '.') {
                result << c;
                i++;
                c = expr[i];
            }
            i--;
            result << " ";
        } else if (isOperator(c)) {
            while (!s.empty() && s.top() != '(' && precedence(s.top()) >= precedence(c)) {
                result << s.top() << " ";
                s.pop();
            }
            s.push(c);
        } else if (isLeftParenthesis(c)) {
            s.push(c);
        } else if (isRightParenthesis(c)) {
            while (!s.empty() && !isLeftParenthesis(s.top())) {
                result << s.top() << " ";
                s.pop();
            }
            s.pop();
        }
    }
    while (!s.empty()) {
        result << s.top() << " ";
        s.pop();
    }
    return result.str();
}

int main() {
    string expr;
    cout << "请输入表达式：";
    getline(cin, expr);
    string postfixExpr = infixToPostfix(expr);
    cout << "后缀表达式：" << postfixExpr << endl;
    double result = evaluatePostfix(postfixExpr);
    cout << "计算结果：" << result << endl;
    return 0;
}

使用时，输入表达式，例如：

(2 + 3) * 4.5 - 1.5 / 3

程序会输出转换后的后缀表达式和计算结果。