在循环使用scanf函数 [英] Using scanf in a while loop

问题描述

大概是一个非常简单的答案，这非常简单的问题：

Probably an extremely simple answer to this extremely simple question:

我在读C的Primer Plus的Pratta，他一直使用的例子

I'm reading "C Primer Plus" by Pratta and he keeps using the example

while (scanf("%d", &num) == 1)...

时的== 1真的有必要吗？这似乎是人们可以这样写：

Is the == 1 really necessary? It seems like one could just write:

while (scanf("%d", &num))

这似乎是平等的测试是不必要的，因为scanf函数的对象读取和1将使while循环真正返回数字。为确保读元素的数量正好是1或者是原因，这完全是多余的？

It seems like the equality test is unnecessary since scanf returns the number of objects read and 1 would make the while loop true. Is the reason to make sure that the number of elements read is exactly 1 or is this totally superfluous?

推荐答案

在C，0被评估为假，一切为true。因此，如果scanf函数返回EOF，这是一个负值，循环将评估为true，这是你想要不是什么。

In C, 0 is evaluated to false and everything else to true. Thus, if scanf returned EOF, which is a negative value, the loop would evaluate to true, which is not what you'd want.

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