Variables

Imagine you're solving a problem and need to store a student's age, marks, or name. The computer also needs a place to store these values.

That's where variables come in.

What is a Variable?

A variable is a named memory location used to store a value that can change during program execution.

For example:

int age = 20;

Here:

• int → data type

• age → variable name

• 20 → value

You can think of a variable like a labeled box.

       age
    ┌────────┐
    │   20   │
    └────────┘

The label is age, and the value stored inside it is 20.

Declaring a Variable

Before using a variable, we generally declare it by specifying its data type and name.

int age;

Here, we have created an integer variable named age.

We can assign a value later:

age = 20;

Or we can do both at once:

int age = 20;

This is called initialization.

Changing a Variable's Value

One important feature of a variable is that its value can change.

int age = 20;

age = 21;

Initially, age contains 20. Later, it contains 21.

That's why it is called a variable—its value can vary.

Multiple Variables

We can create multiple variables in the same program:

int age = 20;
float height = 5.8;
char grade = 'A';

Each variable stores a different type of value.

We'll learn these data types in detail in the Data Types topic.

Rules for Naming Variables

There are a few basic rules you need to follow:

• A variable name can contain letters, digits, and _.

• It cannot start with a digit.

• Spaces are not allowed.

• C keywords cannot be used as variable names.

• C is case-sensitive.

For example:

int studentAge;   // valid
int student_age;  // valid
int age2;         // valid

But:

int 2age;         // invalid
int student age;  // invalid

Also, age and Age are considered different variable names.

Simple Example

#include <stdio.h>

int main()
{
    int age = 20;

    printf("Age = %d", age);

    return 0;
}

Output:

Age = 20

Here, the variable age stores 20, and printf() displays that value.

In Simple Words

You can remember a variable as:

A variable is a named storage location in memory whose value can change during program execution.

For example, a student's marks might change from 70 to 85, so we can store them in a variable.

Once variables are clear, the next important question is: what kind of values can a variable store? That's where Data Types in C come in.