'for'循环后分号的影响 [英] Effect of semicolon after 'for' loop

问题描述

说，我想用为循环用C打印消息五次。为什么，如果我后添加一个分号for循环是这样的：

Say I want to print a message in C five times using a for loop. Why is it that if I add a semicolon after for loop like this:

for (i=0;i<5;i++);

该消息不打印5次，但如果我不把分号那里呢？

the message does not get printed 5 times, but it does if I do not put the semicolon there?

推荐答案

分号是所谓合法声明的空语句的 ^* ，表示什么都不做。因为为循环执行一个单一的操作（这可能是块放在 {} ）分号被视为循环体，导致在你所观察到的行为。

Semicolon is a legitimate statement called null statement ^* that means "do nothing". Since the for loop executes a single operation (which could be a block enclosed in {}) semicolon is treated as the body of the loop, resulting in the behavior that you observed.

以下code

 for (i=0;i<5;i++);
 {
     printf("hello\n");
 }

是国际preTED如下：

is interpreted as follows:

• 重复五次为（i = 0;我小于5;我++）


• ...什么都不做（分号）


• 打开局部变量新的作用域 {


• ...打印你好


• 关闭范围}

• Repeat five times for (i=0;i<5;i++)
• ... do nothing (semicolon)
• Open a new scope for local variables {
• ... Print "hello"
• Close the scope }

正如你所看到的，是被重复操作; ，而不是的printf 。

---

^* 请参见 K＆安培; R ，第1.5.2节

As you can see, the operation that gets repeated is ;, not the printf.

---

^* See K&R, section 1.5.2

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