What are the conditions for user identification to conform to the law in C language?
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The user ID conforms to the conditions of the law: 1, it can only be composed of letters (A to Z), numbers (0 to 9) and the underscore "_", and the first character must be a letter or an underscore, not a number; 2, identifiers cannot use keywords (reserved words).
The operating environment of this tutorial: windows7 system, C99 version, Dell G3 computer.
User identifier:
An identifier defined by the user as needed. It is generally used to name variables, functions, arrays, etc. If the user identifier is the same as the keyword, there will be an error at compile time; if it is the same as the predefined identifier, there will be no error at compile time, but the original meaning of the predefined identifier will be lost, or it may cause an error in the result. therefore, predefined identifiers are generally not used as user identifiers.
User identifiers should generally follow the following naming rules:
1. Identifiers can only consist of letters (AbeliZ, aqz), numbers (0,9) and underscores (_), and the first character must be a letter or underscore, not a number.
2. Keywords have special meaning and cannot be used as identifiers
The following are legal identifiers:
A, x, x3, BOOK_1, sum5
The following is an illegal identifier:
3s cannot start with a number
Illegal character appears in sprinter *
-3x cannot start with a minus sign (-)
Illegal character minus sign appears in bowy-1 (-)
Note:
In C, identifiers are case-sensitive; for example, BOOK and book are two different identifiers.
The length of the identifier should be within 31 characters in c89 and 63 characters in c99.
It is best to take a string with a certain meaning to facilitate memory and understanding of the custom identifier.
Although identifiers can be defined by programmers at will, identifiers are symbols used to identify a certain quantity, so naming should have corresponding meaning as far as possible so that it can be read and understood "as the name implies".
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