带有终止字符的 C++ 切换案例计算器

Question

我正在尝试制作一个 switch case 计算器，它将要求一个表达式（例如 2+2）并打印答案，重复该过程直到用户输入“q”。

当用户输入“q”时，我不知道如何让程序结束。下面的程序成功地要求一个表达，给出答案，并要求另一个。但是，当您输入错误的表达式时，它将永远重复默认情况，包括您输入“q”时。

我知道问题与我如何输入变量有关，考虑到操作数是 double 类型，而且 while 循环也有问题，但我想不出任何替代方案，而且似乎找不到其他地方的解决方案。

int main() {

double operand1;
double operand2;
char operation;
double answer;

while (operation != 'q'){

cout << "Enter an expression:""\n";
cin >> operand1 >> operation >> operand2;


     switch(operation)
{
    case '+':
        answer = (operand1 + operand2);
        break;

    case '-':
        answer = (operand1 - operand2);
        break;

    case '*':
        answer = (operand1 * operand2);
        break;

    case '/':
        answer = (operand1 / operand2);
        break;


    default:
            cout << "Not an operation :/";
            return 0;

}

    cout <<operand1<<operation<<operand2<< "=" << answer<< endl;

}
 return 0;
}

Answer 1

由于您一次读取 3 个变量，当您在控制台中键入 q 时，它被分配给 operand1，而不是 operation，它是 while 循环的终止符 - 因此，无限循环开始。

基本问题在于应用程序的逻辑。该代码的最快解决方案如下：

int main() {

    double operand1;
    double operand2;
    char operation;
    char more = 'y';
    double answer;

    while (more != 'n') {

        cout << "Enter an expression:""\n";
        cin >> operand1 >> operation >> operand2;

        switch (operation)
        {
        case '+':
            answer = (operand1 + operand2);
            break;

        case '-':
            answer = (operand1 - operand2);
            break;

        case '*':
            answer = (operand1 * operand2);
            break;

        case '/':
            answer = (operand1 / operand2);
            break;


        default:
            cout << "Not an operation :/";
            return 0;

        }

        cout << operand1 << operation << operand2 << "=" << answer << endl;
        cout << "Continue? (y/n) ";
        cin >> more;
    }
    return 0;
}

Answer 2

一个简单的改变将解决问题：

int main()
{

    double operand1;
    double operand2;
    char operation = '8';
    double answer;


    while (operation != 'q'){

        cout << "Enter an expression:""\n";
        cin >> operand1 >> operation >> operand2;    
        switch(operation)
        {
            case '+':
                answer = (operand1 + operand2);
                break;

            case '-':
                answer = (operand1 - operand2);
                break;

            case '*':
                answer = (operand1 * operand2);
                break;

            case '/':
                answer = (operand1 / operand2);
                break;


            default:
                    cout << "Not an operation :/";
                    return 0;

        }

        cout <<operand1<<operation<<operand2<< "=" << answer<< endl;

        cout << "Wants to quit? Enter (q)"\n";
        cin >> operation;

    }
 return 0;
}