我无法输入任何字符 [关闭]

问：

假设我写了这个：

std::cout << "Enter either (+ - * /): ";
std::cin >> op;

按下运行代码后：

输入 （+ - * /）：

我无法输入任何字符（+、-、*、/），为什么？

我尝试创建一个基本的计算器：

# include <iostream>

int main() {

    char op;
    double num1;
    double num2;
    double result;

    std::cout << "********** CALCULATOR **********\n";
    
    std::cout << "Enter either (+ - * /): ";
    std::cin >> op;


    std::cout << "Enter #1: ";
    std::cin >> num1;

    std::cout << "Enter #2: ";
    std::cin >> num2;

    switch(op){
        case '+':
            result = num1 + num2;
            std::cout << "Result: " << result << '\n';
            break;

        case '-':
            result = num1 - num2;
            std::cout << "Result: " << result << '\n';
            break;

        case '*':
            result = num1 * num2;
            std::cout << "Result: " << result << '\n';
            break;

        case '/':
            result = num1 / num2;
            std::cout << "Result: " << result << '\n';
            break;
        default:
            std::cout << "That wasn't a valid response\n";
            break;


        
    }


    std::cout << "******************************";

    return 0;
}