Question

我在C ++中创建了一个程序，要求输入任何整数。程序仅在2次迭代后崩溃。代码如下：

#include<iostream>

int main()
{   
    int user_choice;
    std::cout <<"Please enter any number other than five: ";
    std::cin >> user_choice;

    while(user_choice != 5)
    {
        std::cout <<"Please enter any number other than five: ";
        std::cin >> user_choice;
        if(user_choice == 5)
            std::cout << "Program Crash";
            break;
    }
    std::cout << "I told you not to enter 5!";
    return 0;
}

然后我尝试这样做：

if(user_choice == 5)
    std::cout << "Program Crash";
    //std::cout << "Shutting Down";

哪个有效。为什么注释掉第二行，导致程序正常运行？

Answer 1

此代码：

if (counter == 10)
    std::cout << "Wow you still have not entered 5. You win!";
    user_choice = right_answer;

相当于：

if (counter == 10)
{
    std::cout << "Wow you still have not entered 5. You win!";
}
user_choice = right_answer;

您的问题变得明显，user_choice = right_answer仅在counter == 10时才会执行。因此，将其移到if () { ... }块内：

if (counter == 10)
{
    std::cout << "Wow you still have not entered 5. You win!";
    user_choice = right_answer;
}

Answer 2

C ++不尊重缩进;所以当你写：

if (counter == 10)
    std::cout << "Wow you still have not entered 5. You win!";
    user_choice = right_answer;

编译器看到：

if (counter == 10)
    std::cout << "Wow you still have not entered 5. You win!";
user_choice = right_answer;

要将两个陈述放在if下，您需要大括号：

if (counter == 10) {
    std::cout << "Wow you still have not entered 5. You win!";
    user_choice = right_answer; 
}

if语句只运行一个语句

2 个答案: