Variables, Format Specifiers Of C

C Variables – Complete Guide

1. What is a Variable?

A variable in C is a named memory location used to store data. A variable has:

• Data Type – defines what kind of data it can store.
• Name – the identifier.
• Value – the stored data.

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2. Declaring and Initializing Variables

Declaration – Reserves memory:

int age;   // no value yet

Initialization – Assigns a value:

age = 25;

Declaration + Initialization:

int age = 25;        // integer
float gpa = 3.75;    // floating-point
char grade = 'A';    // single character
char name[] = "Bro"; // string (array of characters)

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3. C Data Types (Basic)

Data Type	Example	Typical Size*
int	42	4 bytes
float	3.14	4 bytes
double	3.14159	8 bytes
char	‘A’	1 byte
_Bool	0 / 1	1 byte

*Size may vary depending on system and compiler.

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4. Variable Scope

Scope defines where a variable can be accessed.

1. Local Variables – Declared inside functions; exist only within that function.

void func() {
    int x = 5; // local
}

1. Global Variables – Declared outside all functions; accessible from anywhere.

int g = 10; // global

1. Block Scope – Declared inside {}; accessible only inside that block.

if (1) {
    int y = 20; // block scope
}

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5. Storage Classes

Storage classes define lifetime and visibility.

Keyword	Meaning
auto	Default for local variables.
static	Retains value between function calls.
extern	Declared in another file.
register	Suggests storing in CPU register (faster access).

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6. Constants

Constants store fixed values that cannot change.

const float PI = 3.14;   // constant variable
#define MAX 100          // preprocessor constant

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7. Format Specifiers

Used with printf() / scanf() to display or read variables.

Integer

Specifier	Meaning
%d / %i	Signed integer
%u	Unsigned integer
%o	Octal
%x / %X	Hexadecimal

Floating-Point

Specifier	Meaning
%f	Decimal notation
%.nf	Fixed decimal places
%e / %E	Scientific notation
%g / %G	Shortest representation

Character & String

Specifier	Meaning
%c	Single character
%s	String

Pointer

Specifier	Meaning
%p	Memory address

Special

Specifier	Meaning
%%	Prints %

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8. Example Program

#include <stdio.h>

int globalVar = 100; // global variable

int main() {
    int age = 25;           // integer
    float gpa = 3.75;       // float
    char grade = 'A';       // char
    char name[] = "Bro";    // string
    const float PI = 3.14;  // constant

    printf("Name: %s\n", name);
    printf("Age: %d\n", age);
    printf("GPA: %.2f\n", gpa);
    printf("Grade: %c\n", grade);
    printf("PI: %.2f\n", PI);
    printf("Global Var: %d\n", globalVar);
    printf("Memory address of age: %p\n", (void*)&age);

    return 0;
}