問題描述
整個夏天我一直在使用Accelerated C++"來學習 C++，但有一個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.
為什么
int x;
if (cin >> x){}
相當于
cin >> x;
if (cin){}
通過查看代碼，在我看來，我們正在使用 cin 作為變量.但是，我認為這是一個函數(shù).當 x 具有我們在鍵盤中輸入的任何值時，為什么我們可以這樣使用 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?
推薦答案
cin 是 istream 表示標準輸入流.它對應于cstdio 流stdin.操作符 >>> 重載流返回對同一流的引用.流本身可以通過轉換運算符在布爾條件中評估為真或假.
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;
如果一個非數(shù)字值是一個整數(shù)，那么x"是一個整數(shù)將會失敗進入.所以:
where "x" is an int will fail if a non-numeric value is entered. So:
if(cin>>x)
如果您輸入的是字母而不是數(shù)字，將返回 false.
will return false if you enter a letter rather than a digit.
這個關于使用 C++ I/O 的技巧和竅門 的網(wǎng)站也會對您有所幫助.
This website on tips and tricks using C++ I/O will help you too.
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