Identifiers and Keywords

In C programming, identifiers and keywords are fundamental concepts that serve distinct purposes.

Identifiers

Identifiers are names given to various program elements, such as variables, functions, arrays, and structures. They are user-defined names that allow programmers to refer to these elements conveniently.

Rules for Identifiers:

1. Must begin with a letter (A-Z, a-z) or an underscore (_).
2. Subsequent characters can be letters, digits (0-9), or underscores.
3. Cannot use spaces or special characters (like @, #, $, etc.).
4. C is case-sensitive, meaning variable, Variable, and VARIABLE are different identifiers.
5. Identifiers should not be the same as C keywords.

Examples of Valid Identifiers:

• myVariable
• count_1
• _temp

Examples of Invalid Identifiers:

• 1stVariable (cannot start with a digit)
• my-variable (contains a hyphen)
• int (a keyword)

Keywords

Keywords are reserved words that have special meanings in C. They are part of the C language syntax and cannot be used as identifiers. Keywords define the structure and control the flow of the program.

Common C Keywords:

• int: Defines an integer type.
• float: Defines a floating-point type.
• char: Defines a character type.
• return: Exits a function and optionally returns a value.
• if, else: Control flow statements for conditional execution.
• for, while: Loop control statements for iterative execution.
• void: Specifies that a function does not return a value.

Summary

• Identifiers are user-defined names for program elements, following specific naming rules.
• Keywords are reserved words that have predefined meanings in C and cannot be used as identifiers.