请用C++语言，编写一个具有四则运算计算器功能的程序

在C++中，你可以创建一个简单的命令行四则运算计算器。这里是一个基础的示例，使用结构体和函数实现：

#include <iostream>
using namespace std;

// 定义运算符和操作数的数据结构
struct Calculator {
    double num1, num2;
    char operator_; // 运算符
};

// 函数来处理加法、减法、乘法和除法
double performOperation(Calculator calc) {
    switch (calc.operator_) {
        case '+':
            return calc.num1 + calc.num2;
        case '-':
            return calc.num1 - calc.num2;
        case '*':
            return calc.num1 * calc.num2;
        case '/':
            if (calc.num2 != 0) // 防止除数为零错误
                return calc.num1 / calc.num2;
            else
                throw "Error: Division by zero!";
        default:
            throw "Error: Invalid operator!";
    }
}

int main() {
    double num1, num2;
    char op;
    
    cout << "Enter first number: ";
    cin >> num1;
    cout << "Enter second number: ";
    cin >> num2;
    cout << "Choose an operation (+, -, *, /): ";
    cin >> op;

    Calculator calc = {num1, num2, op};
    try {
        double result = performOperation(calc);
        cout << "Result: " << result << endl;
    } catch (const char* msg) {
        cerr << msg << endl;
    }

    return 0;
}