if (cin >> x) - 为什么你可以使用那个条件?
整个夏天我一直在使用Accelerated C++"来学习 C++，但有一个我似乎不太理解的概念.
I have been using "Accelerated C++" to learn C++ over the summer, and there's a concept which I don't seem to understand properly.
为什么
int x;
if (cin >> x){}
相当于
cin >> x;
if (cin){}
通过查看代码，在我看来，我们正在使用 cin 作为变量.但是，我认为这是一个函数.当 x 具有我们在键盘中输入的任何值时，为什么我们可以这样使用 cin?
By looking at the code, it seems to me that we're using cin as a variable. But, I thought it was a function. Why can we use cin in this way when it is x that has whatever value we input into our keyboard?
推荐答案
cin 是 istream 表示标准输入流.它对应于cstdio 流stdin.操作符 >>> 重载流返回对同一流的引用.流本身可以通过转换运算符在布尔条件中评估为真或假.
cin is an object of class istream that represents the standard input stream. It corresponds to the cstdio stream stdin. The operator >>overload for streams return a reference to the same stream. The stream itself can be evaluated in a boolean condition to true or false through a conversion operator.
cin 提供格式化的流提取.操作cin>>x;
cin provides formatted stream extraction. The operation
cin >> x;
如果一个非数字值是一个整数，那么x"是一个整数将会失败进入.所以:
where "x" is an int will fail if a non-numeric value is entered. So:
if(cin>>x)
如果您输入的是字母而不是数字，将返回 false.
will return false if you enter a letter rather than a digit.
这个关于使用 C++ I/O 的技巧和窍门 的网站也会对您有所帮助.
This website on tips and tricks using C++ I/O will help you too.
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