Variables in C

In C programming, a variable is a named location in memory used to store data that can change during program execution.

Simply put, variables allow us to store information, reuse it, modify it, and work with it logically.

Why Variables Are Important

Without variables, programs would be useless. Variables help us:

• Store user input
• Perform calculations
• Reuse values multiple times
• Make programs dynamic instead of fixed

Declaring a Variable

Before using a variable in C, it must be declared. Declaration tells the compiler:

• What type of data the variable will store
• The name of the variable

int age;
float salary;
char grade;

Here:

• int is the data type
• age is the variable name

Initializing Variables

Initialization means assigning a value to a variable.

int age = 25;
float salary = 35000.50;
char grade = 'A';

It is always a good habit to initialize variables before using them.

Rules for Naming Variables

C follows strict rules for variable names:

• Must start with a letter or underscore
• Cannot start with a number
• No spaces allowed
• Only letters, digits, and underscore allowed
• Keywords cannot be used as variable names

Examples:

• Valid: totalMarks, _count, salary1
• Invalid: 1value, total marks, int

Using Variables in a Program

Let us see a practical example where variables are used for calculation.

#include <stdio.h>

int main() {
    int a = 10;
    int b = 20;
    int sum;

    sum = a + b;

    printf("Sum = %d", sum);

    return 0;
}

Here, variables a and b store numbers, and sum stores the result of addition.

Real-World Example

Think of variables like labeled containers.

• age → stores age
• balance → stores bank balance
• score → stores game score

The label (variable name) stays the same, but the value inside can change.

Mini Practice

• Create variables for two numbers
• Calculate their sum and difference
• Print both results

Quick Quiz

Q1. What is a variable?

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

Q2. Why must variables be declared?

Declaration tells the compiler the data type and memory size.

Q3. Which of these is a valid variable name: 1value or value1?

value1 is valid; variable names cannot start with numbers.

Q4. What happens if a variable is used without initialization?

It may contain garbage (unpredictable) values.

Q5. Can a variable value change during program execution?

Yes, variables are designed to store changeable values.