c++ - 如何阻止它无限重复，但仍保持循环？

Question

在第 33 行，有一个 break 来阻止代码无限重复，但我希望它参与 while 循环。

代码:

#include <iostream>
using namespace std;
int main()
{
while (true){
    {
        cout << "This program counts by twos to any number that is inputted by the user." << endl;
        cout << "Input an even number to start counting." << endl;
        int input;
        cin >> input;
        if (!cin.fail())//fails if input is not an integer
        {
            if (input < 0)//makes sure all numbers are positive
            {
                cout << "That is not a positive number. Try again?" << endl;
            }
            else if (input % 2 != 0) // makes sure all numbers are even
            {
                cout << "That is not an even number. Try again?" << endl;
            }
            else{
                for (int i = 0; i <= input; i += 2) //uses a for loop to actually do the counting once you know that the number is even.
                {
                    cout << i << endl;

                }
            }

        }
        if (cin.fail())//returns this when you input anything other than an integer. 
        {
            cout << "That is not a digit, try again." << endl;
            break;
        }
    }
}
return 0;
}

如果你们能帮我找出为什么会重复，那真的很有帮助。

Answer 1

为了退出循环，需要在for循环后添加break语句。如果没有 break，for 循环将执行并打印您的输出，然后控制将落到 while 循环的末尾，它将从循环的顶部开始。

我还建议将 if (cin.fail()) 更改为 else，因为您已经在检查 if (!cin.fail()) 。如果您想再次循环，还需要忽略其余输入并清除错误标志。

您在 while 循环中还有一组额外的括号。通过这些更改，您的代码将是:

#include <iostream>
#include <limits>
using namespace std;
int main()
{
    while (true)
    {
        cout << "This program counts by twos to any number that is inputted by the user." << endl;
        cout << "Input an even number to start counting." << endl;
        int input;
        cin >> input;
        if (!cin.fail())//fails if input is not an integer
        {
            if (input < 0)//makes sure all numbers are positive
            {
                cout << "That is not a positive number. Try again?" << endl;
            }
            else if (input % 2 != 0) // makes sure all numbers are even
            {
                cout << "That is not an even number. Try again?" << endl;
            }
            else{
                for (int i = 0; i <= input; i += 2) //uses a for loop to actually do the counting once you know that the number is even.
                {
                    cout << i << endl;

                }
                break;  // exit the while loop
            }

        }
        else //else when you input anything other than an integer. 
        {
            cout << "That is not a digit, try again." << endl;
            cin.clear();  // reset the error flags
            cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); // clear any extra input
        }
    }
    return 0;
}