02 Variables & Constants

Program me data store karne ke liye hum Variables ka use karte hain.

1. Variables (Dabba) 📦

Variable ek container hai jisme hum value rakhte hain. C me variable banane ka syntax: type variableName = value;

int age = 25;       // Integer (Number)
float price = 99.9; // Decimal (Point wala number)
char grade = 'A';   // Character (Single letter)

Rules for Naming Variables:

1. Naam alphabet (a-z, A-Z) ya underscore (_) se shuru hona chahiye.
2. Number se shuru NAHI ho sakta (1name ❌).
3. Keywords use nahi kar sakte (jaise int, return ❌).

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2. Data Types (Kis tarah ka data?) 🔢

Type	Description	Size (Approx)	Example
int	Poora number (Integer)	2 or 4 bytes	10, -5
float	Point wala number	4 bytes	3.14, 2.5
double	Bada point wala number	8 bytes	3.14159265
char	Ek akshar (Single Quote)	1 byte	'A', 'z', '#'

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3. Constants (Jo badle na) 🗿

Agar aap chahte hain ki variable ki value kabhi change na ho, to const use karein.

const float PI = 3.14;
// PI = 3.15; // Error aayega! Aap isse change nahi kar sakte.

#define Preprocessor

Ek aur tareeka constant banane ka (bina memory use kiye):

#define MAX_SCORE 100

int main() {
    int score = MAX_SCORE; // 100 replace ho jayega
    return 0;
}

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4. Input & Output (printf & scanf) 🗣️

• printf: Screen par dikhane ke liye.
• scanf: User se input lene ke liye.

Format Specifiers:

• %d: Integer
• %f: Float
• %c: Character

#include <stdio.h>

int main() {
    int age;
    printf("Apni age batao: ");
    scanf("%d", &age); // & zaroori hai (Address)

    printf("Aapki age %d hai.", age);
    return 0;
}