计算器！！！

#include <iostream>
#include <cmath>
using namespace std;

double calculate(double a, double b, char op) {
    switch(op) {
        case '+': return a + b;
        case '-': return a - b;
        case '*': return a * b;
        case '/':
            if (b != 0) return a / b;
            cerr << "错误：除数不能为0！"; 
            return NAN;
        case '^': return pow(a, b);
        default:
            cerr << "错误：无效运算符！";
            return NAN;
    }
}

int main() {
    double num1, num2;
    char op, choice;

    do {
        cout << "\n输入算式 (例：2 + 3): ";
        cin >> num1 >> op >> num2;

        double result = calculate(num1, num2, op);
        if (!isnan(result)) {
            cout << "结果: " << num1 << " " << op << " " << num2 
                 << " = " << result << endl;
        }

        cout << "继续计算？(y/n): ";
        cin >> choice;
    } while(tolower(choice) == 'y');

    cout << "感谢使用计算器！" << endl;
    return 0;
}