Variables and Data Types in C

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Last Updated on: 9th Jul 2025 13:37:41 PM

In C programming, variables are used to store data temporarily in memory, and data types define what kind of data a variable can hold — such as integers, floating-point numbers, characters, etc.

 

1. What is a Variable?

A variable is a named memory location that stores a value which can be changed during program execution.

 

Rules for Naming Variables (Identifiers):

• Must start with a letter (A–Z or a–z) or an underscore _

• Cannot start with a digit (e.g., 1total ?)

• Cannot be a keyword (e.g., int, return)

• Should be meaningful and readable

 

2. Variable Declaration and Initialization

 

Declaration:

Before using a variable, you must declare it by specifying its data type.

 

int age;       // Declares an integer variable named 'age'

 

Initialization:

Assigning a value at the time of declaration.

 

int age = 25;  // Declares and initializes 'age' with 25

 

You can also assign values later:

int age;
age = 25;

 

3. Data Types in C

Data Type	Description	Size (on most systems)	Format Specifier
int	Stores integers (whole numbers)	4 bytes	%d
float	Stores decimal numbers	4 bytes	%f
double	Stores large decimal numbers (higher precision)	8 bytes	%lf
char	Stores a single character	1 byte	%c
void	Represents no value (used in functions)	0 bytes	—

 

Examples: 

int age = 30;           // Integer
float price = 99.99;    // Decimal number
char grade = 'A';       // Character

 

Multiple Variable Declaration:

int x = 10, y = 20, z = 30;

 

4. Type Conversion and Type Casting

Sometimes you need to convert one data type into another, either automatically or manually.

 

a. Implicit Type Conversion (Automatic)

C automatically converts lower data types to higher to prevent data loss.

 

int a = 10;
float b = a;  // int is automatically converted to float

 

Here, a becomes 10.0 and is stored in b.

 

b. Explicit Type Casting (Manual Conversion)

You can manually convert one data type to another using casting syntax:

 

float x = 5.5;
int y = (int) x;   // x is cast to int, value becomes 5

 

Print Now

printf("x = %f, y = %d", x, y);

 

Output:

x = 5.500000, y = 5

 

Example Program:

#include <stdio.h>

int main() {
    int a = 10;
    float b = 3.5;
    float result = a + b;  // Implicit conversion

    printf("Result: %.2f\n", result);

    int x = (int)b;        // Explicit conversion
    printf("After casting b to int: %d", x);

    return 0;
}

 

Quick Summary :

Concept	Description
Variable	A named memory location that holds data
Data Type	Defines the type of data a variable can store
Declaration	Tells the compiler to reserve memory
Initialization	Assigns a value to a variable
Implicit Conversion	Auto-conversion by compiler
Explicit Casting	Manual conversion using (type) syntax

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