> ## 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.

# Identifier

> Rules and examples for naming identifiers in C

# Identifier in C

An **identifier** is the name used to identify variables, functions, arrays, structures, and other user-defined entities in a C program.

Think of a contact list on your phone — the contact name is the identifier, and the phone number is the value stored at that name. Similarly, an identifier gives a name to a memory location.

***

## Rules for Identifiers

* Can contain **letters** (A–Z, a–z), **digits** (0–9), and **underscore** (`_`)
* Must **begin with a letter or underscore** — not a digit
* **Cannot be a C keyword** (e.g. `int`, `for`, `while`)
* Are **case-sensitive** — `total`, `Total`, and `TOTAL` are three different identifiers
* **No special characters** allowed (`@`, `$`, `%`, `#`, etc.)
* No spaces allowed in an identifier name

***

## Valid vs Invalid Identifiers

| Identifier | Valid?    | Reason              |
| ---------- | --------- | ------------------- |
| `age`      | ✅ Valid   | Letters only        |
| `_salary`  | ✅ Valid   | Starts with `_`     |
| `num1`     | ✅ Valid   | Letter then digit   |
| `1num`     | ❌ Invalid | Starts with a digit |
| `int`      | ❌ Invalid | Reserved keyword    |
| `my var`   | ❌ Invalid | Contains a space    |
| `@value`   | ❌ Invalid | Special character   |

***

## Example

```c theme={null}
int age = 25;
float salary = 50000.50;
char grade = 'A';
```

Here, `age`, `salary`, and `grade` are **identifiers** — each names a memory location that stores its respective value.

***

## Key Point

Identifiers are **case-sensitive** in C. This means:

```c theme={null}
int total = 10;
int Total = 20;
int TOTAL = 30;
// All three are different variables!
```