Keywords in C

Keywords are reserved words that have a special, predefined meaning in the C language. You cannot use them as identifiers (variable names, function names, etc.) because the compiler treats them as part of its syntax. There are 32 keywords defined in ANSI C.

List of C Keywords


`auto`	`break`
`case`	`char`
`const`	`continue`
`default`	`do`
`double`	`else`
`enum`	`extern`
`float`	`for`
`goto`	`if`
`int`	`long`
`register`	`return`
`short`	`signed`
`sizeof`	`static`
`struct`	`switch`
`typedef`	`union`
`unsigned`	`void`
`volatile`	`while`

Example

int register;   // ❌ Invalid — 'register' is a keyword
int reg;        // ✅ Valid

Common Keywords and Their Uses

Keyword	Use
`int`, `float`, `char`, `double`	Data type declarations
`if`, `else`, `switch`, `case`	Decision making
`for`, `while`, `do`	Looping
`break`, `continue`, `return`, `goto`	Jump statements
`struct`, `union`, `enum`	User-defined data types
`const`	Declare a constant value
`void`	No return value / no parameters
`sizeof`	Get size of a data type or variable

Keywords are always lowercase in C. Writing INT or While is not a keyword — it would be treated as an identifier.