如何从用户处获取一个号码
我刚刚学习 C，到目前为止，我一直在使用 javascript 和 php 等语言，但我很难将我的一些思维步骤转换为 C 的可能性。我正在编写的程序（听起来比实际要大）使用输入菜单让用户选择一个选项。选项可以是 1、2 或 3。
现在，我正在做：
int menu;
scanf("%d", &menu);
哪个效果很好。但是，输入字符串的字符会导致问题。
在 javascript 中，我只需将菜单变量与选项进行匹配：
if ( menu != 1 && menu != 2 && menu != 3 ){
menu = 4; // a switch later on will catch this.
}
但是，这在 C 中似乎不起作用。
我应该如何处理这个问题？
I'm just learning C, and having worked with languages as javascript and php up till now, i am having trouble converting some of my thinking steps to the possibilities of C. The program i am writing ( that sounds bigger than it really is ) uses an input menu that lets the user pick an option. The options can be 1, 2 or 3.
Now, i'm doing:
int menu;
scanf("%d", &menu);
Which works fine. However, entering a character of a string will cause problems.
In javascript i'd simply match the menu variable against the options:
if ( menu != 1 && menu != 2 && menu != 3 ){
menu = 4; // a switch later on will catch this.
}
However, that does not seem to work in C.
How should i approach this?
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您应该检查错误：（
成功时，
scanf返回您想要读取的项目数。）如何处理错误取决于您。您可以循环直到获得有效值，或者立即中止，或者将变量设置为默认值。另一种方法是使用
fgets读取整行输入，然后尝试对其进行标记和解释，例如使用strtok和strtol。You should check for errors:
(On success,
scanfreturns the number of items that you wanted to read.) How you handle the error is up to you. You could loop until you have a valid value, or abort immediately, or set the variable to a default value.An alternative is to read a whole line of input with
fgetsand then attempt to tokenize and interpret that, e.g. withstrtokandstrtol.scanf 函数返回一个结果，即成功读取输入的计数。 （还有
%n格式序列来获取消耗的字符数。）。所以您可以使用任一解决方案。
或者也许：
我的第二个例子对于你的情况来说并不是很有用。但有时
%n非常有用。我故意在
%d之前放置一个空格：C 库会跳过空格。The scanf function is returning a result, the count of successfully read inputs. (And there is also the
%nformat sequence to get the number of consumed characters.).So you could use either solutions.
or perhaps :
My second example is not really useful in your case. But sometimes
%nis very useful.I am putting a space before the
%don purpose: the C library would skip spaces.