第一项限制是使用的格式，它必须是单条语句或者块。

The first restriction is the actual format, which must be a single statement or block.

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while语句应如以下格式。

A while statement should have the following form.

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switch语句应如以下格式。

A switch statement should have the following form.

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do语句应如以下格式。

A do statement should have the following form.

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try语句应如以下格式。

The try class of statements should have the following form.

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for语句应如以下格式。

A for class of statements should have the following form.

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if语句应如以下格式

The if class of statements should have the following form

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if语句应如以下格式

The if class of statements should have the following form

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