C Variables
What are Variables in C?
Variables are used to store data in a program. A variable acts like a container that holds information which can be used and modified during program execution.
Each variable has:
• A name
• A data type
• A value
Before using a variable in C, it must be declared with a suitable data type.
Example
int age = 20;
Here,
• int is the data type
• age is the variable name
• 20 is the value stored in the variable
Rules for Naming Variables
A variable name in C must follow certain rules:
• It can contain letters, digits, and underscore (_)
• It cannot start with a digit
• It cannot contain spaces
• It cannot use C keywords such as int, float, if, while, etc.
• Variable names should be meaningful and easy to understand
Valid Variable Names:
✓ age
✓ student_name
✓ totalMarks
✓ num1
Invalid Variable Names:
✗ 1age
✗ student name
✗ int
✗ total-marks
Variable Declaration
A variable must be declared before it is used in a program.
Syntax:
data_type variable_name;
int age;
float salary;
char grade;
Explanation
• int age; → Declares an integer variable named age.
• float salary; → Declares a floating-point variable named salary that can store decimal values.
• char grade; → Declares a character variable named grade that can store a single character.
These variables are declared but no values are assigned yet.
Variable Initialization
Variable initialization means assigning a value to a variable at the time of declaration.
Syntax
data_type variable_name = value;
Example
int age = 20;
float salary = 25000.50;
char grade = ‘A’;
Explanation
• int age = 20; → Initializes the variable age with the value 20.
• float salary = 25000.50; → Initializes the variable salary with the value 25000.50.
• char grade = ‘A’; → Initializes the variable grade with the character A.
Example Program
Program
#include <stdio.h>
int main()
{
int age = 20;
printf(“Age = %d”, age);
return 0;
}
Output
Age = 20
Explanation
• #include <stdio.h> → Includes the standard input/output library.
• int main() → Starting point of the program execution.
• int age = 20; → Declares and initializes an integer variable named age with value 20.
• printf(“Age = %d”, age); → Displays the value stored in the variable age.
• %d → Format specifier used to print integer values.
• return 0; → Terminates the program successfully.
Key Points
• Variables are used to store data in a program.
• Every variable must have a data type.
• Variable names must follow naming rules.
• Variables should be declared before they are used.
• Variables can be initialized at the time of declaration.
• Meaningful variable names make programs easier to understand.