> ## Documentation Index
> Fetch the complete documentation index at: https://learn.acadlink.app/llms.txt
> Use this file to discover all available pages before exploring further.

# Keywords

> Reserved keywords in C and their significance

# 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

```c theme={null}
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 |

<Note>
  Keywords are always **lowercase** in C. Writing `INT` or `While` is not a keyword — it would be treated as an identifier.
</Note>