What are the naming rules for user identifiers in C language

The naming rules for user identifiers in C language are: 1. User identifiers must start with the letters a~z, A~Z or an underscore; 2. User identifiers are case-sensitive; 3. C language Keywords in have special meaning and cannot be used as identifiers.

User identifiers in C language should generally follow the following naming rules:

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1. The identifier must start with the letters a~z, A~Z or an underscore, and can be followed by any number (can be 0) characters. These characters can be letters, underscores, numbers, and other characters. It is not allowed to appear in the identifier;

2. Identifiers are case-sensitive;

3. The length of the identifier, c89 stipulates that it should be within 31 characters, and c99 stipulates that it should be within 63 characters;

4. Keywords in C language have special meanings and cannot be used as identifiers;

5. It is best to use a string with a certain meaning for a custom identifier to facilitate memory and understanding.

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