Rust 程序（主要）由一系列语句组成：
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Rust 中有几种语句。最常见的两种是声明变量绑定，以及在表达式后使用分号 ;：
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代码块也是表达式，因此可以在赋值中作为值使用。代码块中的最后一个表达式会被赋值给左值表达式（如局部变量）。但是，如果代码块的最后一个表达式以分号结尾，返回值将是 ()。
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