异常是在程序运行时发生的不正常情况。

An exception is an abnormal situation that happens while a program is running.

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变量为数据提供占位，使得其可以在程序运行时改变。

Variables serve as placeholders for data that can change during the execution of a program.

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最后，在程序运行时，可以使用' set '命令修改变量的值。

Finally you can modify the values of variables whilst a program is running using the 'set' command.

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