C Variables

1. What is a Variable?

• A variable is a named memory location used to store data.

• Each variable has:

  1. Name (Identifier) → The name you give it.

  2. Data Type → The type of data it can store (int, float, char, etc.).

  3. Value → The actual data stored.

Example:

2. Rules for Naming Variables

1. Must start with a letter or underscore (_).

2. Can contain letters, digits, and underscores.

3. Cannot be a C keyword (like int, float, return).

4. Case-sensitive (Age ≠ age).

Valid Examples:

Invalid Examples:

3. Variable Declaration and Initialization

(a) Declaration

• Tells the compiler the type and name of a variable.

(b) Initialization

• Assigns a value at the time of declaration.

• You can also assign a value later:

4. Data Types of Variables

C has basic data types:

• int → Integer numbers

• float → Decimal numbers

• double → More precise decimal numbers

• char → Single character

5. Multiple Variables Declaration

You can declare multiple variables of the same type in a single line:

6. Constants vs Variables

• Variables → Value can change.

• Constants → Value cannot change. Use const keyword.

7. Example Program Using Variables

Output:

8. Tips

1. Always choose meaningful names (age instead of a).

2. Use consistent naming convention (like snake_case or camelCase).

3. Remember C is case-sensitive.