用C重复程序功能衰竭，scanf函数关系吗？ [英] repeat program function failure in C, scanf related?

问题描述

所以我想询问用户是否愿意重复我的计划，现在，然后我得到一个奇怪的结果。它不会发生，每次我没有带能够找出什么触发了。

So I'm trying to ask the user if they would like to repeat my program and I am getting a weird result now and then. It doesn't happen everytime and I havn't been able to figure out what triggers it.

要我来说，它看起来像它后，我输入Q以repeatProgram，而不是'Q'被分配'回归'，但我不知道为什么。

To me it looks like it is assigning the 'return' after I enter 'q' to repeatProgram instead of the 'q' but I have no Idea why.

输出时，它的工作原理：

The output when it works:

的退出输入q，继续输入y。的

小号

的您输入S，这不是一个有效的选项。的

输出当它失败：

的退出输入q，继续输入y。的

q

的您输入的

，这不是一个有效的选项。的

在code：

char RepeatProgramPrompt()
{
    char repeatProgram;

    do
    {
        printf("\nTo exit enter q, to continue enter y.\n");
        scanf("%c%*c", &repeatProgram);

        repeatProgram = tolower(repeatProgram);

        if(repeatProgram != 'y' && repeatProgram != 'q')
        {
            printf("\nYou've entered %c, that isn't a valid option.\n", repeatProgram);

        }

    }while(repeatProgram != 'y' && repeatProgram != 'q');


    return(repeatProgram);
}

所以我的问题是，为什么会出现这种情况？它会正常工作了一堆的尝试，然后就失败。

So my question is, why is this happening? it will work fine for a bunch of tries and then just fail.

很抱歉，如果我格式化这个错误是我的第一篇文章。

Sorry if I've formatted this wrong it is my first post.

推荐答案

出现这个问题，因为你的 scanf函数读 \\ n 您第一次输入之后。为了避免这种情况的改变你的 scanf函数声明如下：

That problem occurs because your scanf reads the \n after your first input. To avoid this change your scanf statement to this:

scanf("%c", &repeatProgram);
getchar(); // this will remove the excess '\n'

输出：

Sukhvir@Sukhvir-PC ~
$ ./test

To exit enter q, to continue enter y.
d

You've entered d, that isn't a valid option.

To exit enter q, to continue enter y.
s

You've entered s, that isn't a valid option.

To exit enter q, to continue enter y.
d

You've entered d, that isn't a valid option.

To exit enter q, to continue enter y.
q

Sukhvir@Sukhvir-PC ~
$

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