What are keywords in the C language?

In C language, keywords are reserved words with special meanings used to represent specific syntax structures or functions. These keywords have special purposes in C language and cannot be used as identifiers (variable names, function names, etc.).

Keywords in the C programming language include:

1. Keywords for data types, such as int, char, float, and double, are used to declare the data type of variables.
2. Control statement keywords such as if, else, switch, case, default, for, while, and do are used to control the flow of execution in a program.
3. Storage class keywords such as auto, extern, static, and register are used to control the storage and lifetime of variables.
4. Function keywords such as void and return are used to specify the return type and return value of a function.
5. File operation keywords such as FILE, fopen, fclose, fread, fwrite, etc., are used for performing file read and write operations.
6. Pointer keywords such as int *, char * are used to define pointer variables.
7. Keywords for struct, union, typedef, etc. are used to define structure and union types.
8. Other keywords such as sizeof and enum are used to obtain the size of variables or define enumeration types.

It is important to note that keywords are a part of the C language and cannot be redefined or changed in meaning. Therefore, when writing C programs, it is best to avoid using keywords as identifiers.