while（getchar（）！='\\\<br/>'）; [英] while (getchar () != &#39;\n&#39; );

问题描述

我有以下for循环，我提示用户输入一个4位数的引脚，然后按回车。有人可以向我解释什么是while循环，因为我不完全理解它。

$ p $ //用户输入引脚
（i = 0; i< PIN_LENGTH; i ++）
{
printf（输入PIN的数字％d，i）;
user_pin [i] = getchar（）;
while（getchar（）！='\\\
'）; //这行是干什么的？

$ / code>

解决方案

循环从 stdin 丢弃不需要的字符，以便下一个输入函数有一个干净的流，特别是丢弃 \ n getchar（）返回 EOF ，所以循环应该测试 EOF 也是如此：

  int ch; （（ch = getchar（））！='\ n'&& ch！= EOF）
 continue; //放弃不需要的字符
  

还要注意，如果 stdin 已被重定向，可以在不遇到 \\\
的情况下达到 EOF 。而@chqrlie在评论中指出，用户可以通过输入 Ctrl-D 来从终端发信号给 EOF >在Linux中，或在Windows中 Ctrl-Z 。因此显式测试 EOF 的重要性。

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() != '\n'); //what is this line doing??
}

解决方案

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 \n 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()) != '\n' && ch != EOF)
    continue;  // discard unwanted characters

Also note that, if stdin has been redirected, it is possible to reach EOF without encountering a \n. 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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