c++ - for循环没有在while循环中第二次执行

Question

我只是 C++ 的初学者。我正在编写小而简单的程序，打印两个用户指定整数之间的一系列整数。

最后，如果用户返回 1，程序将重新运行 while 循环，但当发生这种情况时，程序将不会再次打印数字系列(for 循环不起作用)。

这是源代码:

int main(void)
{
    int num1, num2;
    int doContinue = 1;

    while (doContinue == 1)
    {
        cout << "Please enter two integers, the first being the smallest: ";

         do { //does everything in curly braces while the user inputs the numbers wrong...
                cin >> num1 >> num2;

                if (num1 > num2)
                    {
                        cout << "Your first number was bigger than the second.\nTry again!: ";
                    }

            } while (num1 > num2);//... but once it's not wrong, break out of this do loop

        //at this point the input has been checked, so we can proceed to print the series

        for(int num1; num1 <= num2; num1++)
            {   
                cout << num1 << " \n";
            }

        cout << "Would you like to compute another series of integers? 1=yes, anything else=no: ";
        cin >> doContinue;
    }

    return 0;
}

Answer 1

您的代码表现出未定义的行为。

    for(int num1; num1 <= num2; num1++)
        {   
            cout << num1 << " \n";
        }

创建一个名为 num1 的新整数, 与 num1 无关在 for 循环之外。您没有初始化 num1 的值, 但继续与它进行比较。

删除 int num1 (也就是说，类似 for(; num1 <= num2; num1++) 的东西)在你的 for 循环中重试。