C Variables

C Tutorial

1. What is a C Variables?

  • In C Variables are 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:

int age = 25; // age is a variable of type int storing 25

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:

int 1age; // starts with digit ❌
float float; // keyword ❌

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:

int age;
age = 25;

4. Data Types of Variables

C has basic data types:

Data Type Memory Size Example
int 4 bytes int age = 25;
float 4 bytes float pi = 3.14;
double 8 bytes double d = 3.14159;
char 1 byte char grade = ‘A’;

  • 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.

const float PI = 3.14159;
// PI = 3.14; // ❌ Not allowed

7. Example Program Using Variables


 

Output:

Age: 25
Height: 5.9
Grade: A

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.

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