这是因为实际的源代码和变量绑定可以更改，这是建立在环境或者构建宏预处理程序指令的时间定义的基础上的。

This is because the actual source code and the variable binding can change, based on the environment or the build time definitions of macros and preprocessor commands.

youdao

需要设置变量是因为(可能在命名模板中)使用了一系列“编程”指令来设置它的值。

You needed to set the variable because you used a sequence of "programming" instructions, possibly in a named template, to set its value.

youdao

在指令序列中使用仅引用一次的局部变量。

Using a local variable declared inside a sequence of instructions that is referenced only once.

youdao

And I want to remind you, that block of code is a set of instructions, the same set of instructions that are going to be done each time through the loop.

我想提醒大家,这块代码是一个指令集,一个每次循环都会被执行的相同指令集,会变化的仅仅是变量的值。

麻省理工公开课 - 计算机科学及编程导论课程节选