Variables and Data Types in C

📘 C 👁 60 views 📅 Dec 22, 2025

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A variable is a named memory location used to store data that can be changed during program execution.

Rules for Naming Variables

Must begin with a letter or underscore _
Can contain letters, digits, and underscores
Cannot start with a digit
Cannot use C keywords
Case-sensitive

Valid: count, _total, sum1
Invalid: 1num, float, total-value

Declaration of Variables

int a;
float b;
char c;

Initialization of Variables

int a = 10;
float b = 5.5;
char c = 'A';

Types of Variables

Local Variables – Declared inside a function
Global Variables – Declared outside all functions
Static Variables – Retain value between function calls
Automatic Variables – Default local variables

Data Types in C

Data types specify the type of data a variable can store.

Classification of Data Types

1. Basic (Primary) Data Types

Data Type	Description
`int`	Integer values
`float`	Decimal values
`double`	Double precision decimals
`char`	Single character

2. Derived Data Types

Arrays
Pointers
Structures
Unions

3. Enumeration Data Type

enum day {Mon, Tue, Wed};

4. Void Data Type

Represents no value

void display();

Size of Data Types (Typical)

Data Type	Size
`char`	1 byte
`int`	2 or 4 bytes
`float`	4 bytes
`double`	8 bytes

Example Program

#include 

int main() {
    int age = 20;
    float salary = 25000.50;
    char grade = 'A';

    printf("%d %.2f %c", age, salary, grade);
    return 0;
}

Summary

Variables store data values
Data types define the kind of data
C supports multiple data types
Proper declaration is mandatory

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