while (getchar() != ' ' ); [英] while (getchar () != ' ' );

问题描述

我有以下 for 循环，我提示用户输入一个 4 位数的 pin 并按回车键.有人可以向我解释 while 循环到底在做什么，因为我不完全理解它.

I have the following for loop, I am prompting the user to enter a 4 digit pin and hit enter. Can someone explain to me what the while loop is really doing because I don't fully understand it.

//user input for pin
for(i = 0; i < PIN_LENGTH; i++)
{
    printf("Enter digit %d of your PIN: ", i);
    user_pin[i] = getchar();
    while (getchar() != '
'); //what is this line doing??
}

推荐答案

正如其他人提到的，这个循环从 stdin 中丢弃不需要的字符，以便下一个输入函数有一个干净的流，特别是它丢弃用户输入的最后一个字符之后的 .但是，getchar() 在读取错误的情况下返回 EOF，因此循环也应测试 EOF，如下所示:>

As mentioned by others, this loop discards unwanted characters from stdin so that the next input function has a clean stream, and in particular it discards the that follows the last character entered by the user. But, getchar() returns EOF in the event of a read error, so the loop should test for EOF also, like this:

int ch;
while ((ch = getchar()) != '
' && ch != EOF)
    continue;  // discard unwanted characters

另请注意，如果 stdin 已被重定向，则可以到达 EOF 而不会遇到 .而且，正如@chqrlie 在评论中指出的那样，用户可以通过在 Linux 中输入 Ctrl-D 或 Ctrl-Z<从终端发出 EOF 信号/code> 在 Windows 中.因此，明确测试 EOF 的重要性.

Also note that, if stdin has been redirected, it is possible to reach EOF without encountering a . And, as @chqrlie pointed out in the comments, the user can signal an EOF from the terminal by entering Ctrl-D in Linux, or Ctrl-Z in Windows. Hence the importance of testing for EOF explicitly.

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