C Tokens, Identifiers, and Keywords: Understanding Tokens and Their Types

What Is a Character Set?

Like any programming language, C has its own character set. A C program is a sequence of instructions that manipulate data composed of characters and symbols. The compiler ignores most formatting characters, but they are essential for human readability.

The C character set is divided into four groups:

• Letters (uppercase A‑Z and lowercase a‑z)
• Numbers (digits 0‑9)
• White space (spaces, tabs, newlines, carriage returns)
• Special characters (punctuation and symbols)

Below is a comprehensive list of the special characters used in C:

What Is a Token in C?

A token is the smallest meaningful unit that the C compiler recognizes. During lexical analysis, the source code is broken down into tokens before parsing and code generation. C tokens fall into six categories:

• Keywords
• Operators
• Strings
• Constants
• Special Characters
• Identifiers

Keywords and Identifiers

Every word in C is either a keyword or an identifier. Keywords are reserved, have fixed meaning, and cannot be reused for naming. Identifiers are user‑defined names for variables, functions, types, and more.

Keywords in C

There are 32 keywords in the C language, all written in lowercase. They are listed below in a tidy table for quick reference:

Identifiers

An identifier is the name you give to a variable, function, structure, enum, etc. The C standard imposes several rules on identifiers:

1. The first character must be a letter (A‑Z, a‑z) or an underscore (_).
2. Subsequent characters may be letters, digits (0‑9), or underscores.
3. Identifiers cannot be any of the 32 keywords.
4. They must not contain whitespace.
5. While not enforced by the compiler, meaningful names improve code readability and maintainability.

Summary

• C tokens are the smallest units the compiler processes.
• Keywords are reserved words with fixed meanings; there are 32 of them.
• Identifiers uniquely name program elements and follow strict naming rules.