Question

我目前正在从事编程工作，在检查用户输入的内容时遇到了麻烦。该程序仅在其中输入两个正数，但是当我输入一个字符（例如“ a”作为我的第一个“数字”）时，程序会接受它并将其输出，就像我输入零一样。它应该输出“无效数字：数字必须为正整数”。有人可以告诉我我在做什么错吗？谢谢！

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Answer 1

if (firstNum==x || secondNum==x)
    cout<< "\nError: Invalid number: Numbers must be positive integer.\n";

此测试是错误的x尚未初始化，并且没有任何意义。.plus您已使用该标志来测试我假设的失败输入情况，因此您的代码应像这样

#include <iostream>
using namespace std;

int main()
{
    //Displays information of what program will do
    cout << "Practice with iterations\n\n"
        << "The function of this program is, given 2 positive numbers, the"
        << " program";
    cout << "\nwill display the following\n\n";

    cout << "\t1. All even numbers between firstNum and secondNum.\n"
        << "\t2. All odd numbers between firstNum and secondNum.\n"
        << "\t3. Sum of all even numbers between firstNum and secondNum.\n"
        << "\t4. Sum of all odd numbers between firstNum and secondNum.\n"
        << "\t5. All prime numbers between firstNum and secondNum.\n"
        << "\t6. Factorial of the secondNum.\n"
        << "\t7. The numbers and their squares between firstNum and "
        << "secondNum." << endl;

    //Declare first and second number variables
    int firstNum;
    int secondNum;
    bool flag = true;    //Set to true

                        //Ask user to input values
    cout << "\n\nEnter the first number:\t\t";
    cin >> firstNum;

    if (cin.fail())
    {
        cin.clear();
        cin.ignore(256, '\n');
        flag = 0;
    }

    cout << "Enter the second number:\t";
    cin >> secondNum;

    if (cin.fail())
    {
        cout << "lol" << endl;
        cin.clear();
        cin.ignore(256, '\n');
        flag = 0;
    }

    if (flag) {
        if (firstNum > secondNum)
            cout << "\nError: First number must be < second number.\n";
        else if (firstNum < 0 || secondNum < 0)
            cout << "\nError: Invalid number: Number must be positive.\n";

        else
        {
            cout << "\nYou entered: " << firstNum << " and " << secondNum;
        }
    }
    else cout << "Error input" << endl;
    return 0;
}

Answer 2

如果在读取输入时出现错误，则说明您已正确说明了第一步-清除输入流并清除cin的错误状态。您缺少的是将有效内容读入变量。为此，您需要一个循环。

while (true )
{
   //Ask user to input values
   cout<< "\n\nEnter the first number:\t\t";

   // Try to read the input. If it is successful, break out of the loop.
   if ( cin>> firstNum )
   {
      break;
   }

   // Clear the error flag. Clear the input stream. Try again.
   cin.clear();
   cin.ignore(256,'\n');
}

对第二个数字做同样的事情。

C ++仅接受正整数

2 个答案: