The compiler distinguishes between uppercase and lowercase letters in identifiers. For example, PROFIT and profit represent different identifiers.
Avoid creating identifiers that begin with an underscore (_) for function names and variable names.
The first character in an identifier must be a letter. The _ (underscore) character is considered a letter; however, identifiers beginning with an underscore are reserved by the compiler for identifiers at global namespace scope.
Identifiers that contain two consecutive underscores or begin with an underscore followed by a capital letter are reserved in all contexts.
The dollar sign can appear in identifier names when compiled using the -qdollar compiler option or at one of the extended language levels that encompasses this option.
You should always include the appropriate headers when using standard library functions.
Although the names of system calls and library functions are not reserved words if you do not include the appropriate headers, avoid using them as identifiers. Duplication of a predefined name can lead to confusion for the maintainers of your code and can cause errors at link time or run time. If you include a library in a program, be aware of the function names in that library to avoid name duplications. You should always include the appropriate headers when using standard library functions.
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