Variables in C

A variable is a named container that occupies a memory location to store a value. That value can be read and changed during program execution.

Declaration and Initialization

Declaration — reserves memory for the variable:

int number;

Initialization — declaration + assigning a value:

int number = 10;

Syntax:

data_type variable_name;
data_type variable_name = value;

Naming Conventions

Style	Example	Used In
Pascal Case	`UserName`	Types, structs
Camel Case	`userName`	Variables, functions
Snake Case	`user_name`	C variables, Python
Kebab Case	`user-name`	Not valid in C

Variable Classification by Data Type

Data Type	Keyword	Size	Range
Character	`char`	1 byte	−128 to 127
Integer	`int`	4 bytes	±2.1 billion
Short Integer	`short`	2 bytes	−32,768 to 32,767
Long Integer	`long`	4–8 bytes	Platform dependent
Float	`float`	4 bytes	±3.4 × 10³⁸
Double	`double`	8 bytes	±1.7 × 10³⁰⁸
Long Double	`long double`	10–16 bytes	Even higher

Variable Classification by Scope

Type	Declared In	Scope	Lifetime
Local	A function/block	That block only	Until block ends
Global	Outside functions	Whole file	Whole program
Static	With `static`	Limited, keeps value	Until program ends
Extern	Another file	Global	Depends on origin
Register	With `register`	CPU register	Until block ends

Format Specifiers

Used with printf() and scanf() to read/print specific types:

Specifier	Data Type	Example Output
`%d`	`int`	`25`
`%f`	`float`	`5.68`
`%lf`	`double`	`3.14`
`%c`	`char`	`A`
`%s`	string	`Hello`

printf("%d", 25);       // 25
printf("%.2f", 5.6789); // 5.68
printf("%.2lf", 3.14);  // 3.14
printf("%c", 'A');      // A
printf("%s", "Hello");  // Hello

Example

#include <stdio.h>

int main() {
    int age = 20;
    float cgpa = 8.75;
    char grade = 'A';

    printf("Age  : %d\n", age);
    printf("CGPA : %.2f\n", cgpa);
    printf("Grade: %c\n", grade);

    return 0;
}

Fundamentals

Functions

Array

String

Structure

Union

Pointer

File Handling

Preprocessor

Variables

Variables in C

Declaration and Initialization

Naming Conventions

Variable Classification by Data Type

Variable Classification by Scope

Format Specifiers

Example

​Variables in C

​Declaration and Initialization

​Naming Conventions

​Variable Classification by Data Type

​Variable Classification by Scope

​Format Specifiers

​Example

Variables in C

Declaration and Initialization

Naming Conventions

Variable Classification by Data Type

Variable Classification by Scope

Format Specifiers

Example