常见的一种特殊情况就是在循环外部声明变量。
One special case that shows up frequently is declaring variables outside of loops.
方法内部声明的变量是局部变量，在方法外部是不能够使用的。
Variables declared with a method are local to that method and cannot be used outside of it.
默认情况下，在文件域中声明变量和函数是外部的。
Declarations of variables and functions at file scope are external by default.
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