1. Integer constant: Integer constant is a constant integer with three representations: decimal, octal and hexadecimal;

2. Real number constants: Real number constants are only expressed in decimal decimal decimal form and exponential form, not in octal and hexadecimal form;

3. Character constants: Character constants must be enclosed in single quotation marks. You can use control characters, single quotes, double quotes, backslashes, and so on.

4. String constant: a sequence of one or more characters enclosed in double quotation marks;

5. Symbolic constant: Identifiers are used to represent constants and must be defined before use.