1, keywords

Keywords, also called reserved words, are some predefined words with fixed meanings in C language, such as int and return in the first program of C language. Users can only use it according to the predefined meaning, and can't change the meaning without authorization.

2. Identifier

Identifiers are divided into system predefined identifiers and user-defined identifiers.

As the name implies, the system predefined identifiers are predefined by the system, such as the main function main and the output function printf. Different from keywords, the system predefined identifiers can be redefined by users, but this will conflict with the original definition and the original meaning will be replaced, so it is not recommended!

User-defined identifiers are identifiers defined by users according to their needs, which are usually used as variable names, function names and so on. There are certain rules for naming identifiers.

3. Operators

First of all, there are 44 operators, so I won't list them here. Then, because operators are widely used and have complex types, here is just a list of classifications. It may take a long time to clarify the real use. So, just know what they are first, and it doesn't matter if you can't remember them. Take it easy!

1, arithmetic operators:+addition,-subtraction, * multiplication,/division,% remainder.

2. relational operators: > greater than, > = = equal to, = = equal to,