c++ - 如何避免用户输入错误的信息？

Question

我是一个非常新手的程序员，所以我不太了解如何编写代码来保护应用程序。基本上，我创建了一个 basicMath.h 文件并创建了一个 do while 循环来制作一个非常基本的控制台计算器(只有两个 float 通过函数传递)。我使用一系列 if 和 else if 语句来确定用户想要执行的操作。 (1.add, 2.subtract, 3.multiply, 4.divide) 我使用了 else { cout << "invalid input"<< endl;} 来防止任何其他值，但后来我尝试实际写一封信，程序进入无限循环。是否有办法防止用户意外击中字符而不是数字？

 `#include <iostream>
  #include "basicMath.h"

  using namespace std;
  char tryAgain = 'y';
  float numOne = 0, numTwo = 0;
  int options = 0;
  int main()
  {
   cout << "welcome to my calculator program." << endl;
 cout << "This will be a basic calculator." << endl;
 do{
    cout << "What would you like to do?" << endl;
    cout << "1. Addition." << endl;
    cout << "2. Subtraction." << endl;
    cout << "3. Multiplication" << endl;
    cout << "4. Division." << endl;
    cin >> options;
    if (options == 1){
        cout << "Enter your first number." << endl;
        cin >> numOne;
        cout << "Enter your second number." << endl;
        cin >> numTwo;
        cout << numOne << " + " << numTwo << " = " << add(numOne, numTwo) << endl;
    }
    else if (options == 2){
        cout << "Enter your first number." << endl;
        cin >> numOne;
        cout << "Enter your second number." << endl;
        cin >> numTwo;
        cout << numOne << " - " << numTwo << " = " << subtract(numOne, numTwo) << endl;
    }
    else if (options == 3){
        cout << "Enter your first number." << endl;
        cin >> numOne;
        cout << "Enter your second number." << endl;
        cin >> numTwo;
        cout << numOne << " * " << numTwo << " = " << multiply(numOne, numTwo) << endl;
    }
    else if (options == 4){
        cout << "Enter your first number." << endl;
        cin >> numOne;
        cout << "Enter your second number." << endl;
        cin >> numTwo;
        cout << numOne << " / " << numTwo << " = " << divide(numOne, numTwo) << endl;
    }
    else {
        cout << "Error, invalid option input." << endl;
    }
    cout << "Would you like to use this calculator again? (y/n)" << endl;
    cin >> tryAgain;
}while (tryAgain == 'y');
cout << "Thank you for using my basic calculator!" << endl;
return 0;
}
 `

Answer 1

一种方法是使用异常处理，但作为新手，您可能还远远没有学会这一点。

而是使用 cin.fail()，它在错误或意外输入后返回 1。请注意，您需要使用 cin.clear() 清除“bad”状态。

一个简单的方法是实现一个函数:

int GetNumber ()
{
    int n;
    cin >> n;
    while (cin.fail())
    {
        cin.clear();
        cin.ignore();
        cout << "Not a valid number. Please reenter: ";
        cin >> n;
    }
    return n;
}

现在，在主函数中，无论您在何处获取输入，只需调用 GetNumber 并将返回值存储在变量中即可。例如，不要使用 cin >> numOne;，而是 numOne = GetNumber();