C & C++ Notes – Chapter 1: Introduction

(English + Hindi)

📌 What is Programming?

English:
Programming is the process of writing instructions for a computer to perform tasks.

Hindi:
Programming वह प्रक्रिया है जिसमें हम कंप्यूटर को काम करने के लिए निर्देश लिखते हैं।

📌 What is C Language?

English:
C is a powerful, structured, and middle-level programming language developed by Dennis Ritchie in 1972 at Bell Labs.

Hindi:
C एक शक्तिशाली, structured और middle-level प्रोग्रामिंग language है, जिसे Dennis Ritchie ने 1972 में Bell Labs में बनाया था।

📌 What is C++?

English:
C++ is an extension of C language with Object-Oriented Programming (OOP) features. Created by Bjarne Stroustrup in 1983.

Hindi:
C++ C भाषा का बढ़ा हुआ रूप है जिसमें Object-Oriented Programming (OOP) फीचर्स जोड़े गए हैं। इसे Bjarne Stroustrup ने 1983 में बनाया।

✅ Key Difference: C vs C++

Feature	C	C++
Type	Procedural	Object-Oriented + Procedural
Approach	Function-based	Object + Function-based
Security	Less	High (Encapsulation)
OOP Support	❌ No	✅ Yes

🧠 Flowchart: Basic Program Flow

   +---------+
   |  Start  |
   +---------+
        |
        v
+------------------+
|  Input Data      |
+------------------+
        |
        v
+------------------+
|  Process (Logic) |
+------------------+
        |
        v
+------------------+
| Output / Result  |
+------------------+
        |
        v
   +---------+
   |  End    |
   +---------+

✅ First Program in C

#include <stdio.h>

int main() {
    printf("Hello World");
    return 0;
}

Output:

Hello World

✅ First Program in C++

#include <iostream>
using namespace std;

int main() {
    cout << "Hello World";
    return 0;
}

Output:

Hello World

📘 Explanation (English + Hindi)

#include – includes library
Hindi: लाइब्रेरी जोड़ना
main() – starting point of program
Hindi: प्रोग्राम यहीं से शुरू होता है
printf / cout – output function
Hindi: स्क्रीन पर मैसेज दिखाता है

📝 Exercises / अभ्यास

✅ Task-1

Write a program to print:

My Name
My College
My Course

Hindi:
एक प्रोग्राम लिखिए जो आपका नाम, कॉलेज और कोर्स दिखाए।

✅ Task-2

Draw a flowchart for “ATM Cash Withdrawal”.

Hindi:
ATM से पैसे निकालने का फ्लोचार्ट बनाइए।

✅ Task-3

Difference between C and C++ (5 points)

Hindi:
C और C++ में 5 अंतर लिखिए।

✨ Ready for Next Chapter?

Available Chapters:

✅ Introduction
Variables & Data Types
Input / Output
Operators
Conditions & Branching
Loops
Functions
Arrays
Pointer vs Reference
Strings
Structures vs Classes
Object-Oriented Concepts (for C++)

📘 Chapter-2: Variables & Data Types

✅ What is a Variable?

English:
A variable is a container used to store data in memory.

Hindi:
Variable एक container होता है जिसमें हम memory में data store करते हैं।

✅ Rules for Naming Variables

English

Must start with a letter or underscore _
No spaces allowed
No special characters except _
Case-sensitive (age ≠ Age)
Can’t use keywords (like int, float, etc.)

Hindi

Variable नाम letter या _ से शुरू होना चाहिए
Space नहीं होना चाहिए
Special characters नहीं होंगे (@,#,% etc.)
Capital & small अलग माने जाते हैं
Keywords variable नाम नहीं हो सकते

✅ Example Variable Declarations

C Language

int age = 20;
float marks = 85.5;
char grade = 'A';

C++ Language

int age = 20;
float marks = 85.5;
char grade = 'A';
string name = "Rahul";

🧠 Flowchart: Using a Variable

+---------+
|  Start  |
+---------+
     |
     v
+-------------+
| Declare Var |
+-------------+
     |
     v
+-------------+
| Assign Data |
+-------------+
     |
     v
+-------------+
| Use/Display |
+-------------+
     |
     v
+---------+
|  End    |
+---------+

✅ What are Data Types?

English:
Data types define the type of data stored in a variable.

Hindi:
Data type यह बताता है कि variable में किस प्रकार का data store होगा।

🧾 Basic Data Types in C / C++

Data Type	Size	Example	Description
`int`	2/4 bytes	`10`	Integer (number without decimal)
`float`	4 bytes	`10.5`	Decimal number
`double`	8 bytes	`123.456`	Large decimal number
`char`	1 byte	`'A'`	Single character
`string` (C++ only)	variable	`"Hello"`	Text

✅ Example Program (C)

#include <stdio.h>

int main() {
    int age = 21;
    float salary = 15000.50;
    char grade = 'A';

    printf("Age = %d\n", age);
    printf("Salary = %f\n", salary);
    printf("Grade = %c\n", grade);

    return 0;
}

✅ Example Program (C++)

#include <iostream>
using namespace std;

int main() {
    int age = 21;
    double salary = 15000.75;
    char grade = 'A';
    string name = "Rohan";

    cout << "Name = " << name << endl;
    cout << "Age = " << age << endl;
    cout << "Salary = " << salary << endl;
    cout << "Grade = " << grade;

    return 0;
}

🏋️‍♂️ Practice Exercises / अभ्यास

✍️ Q1:

Declare variables for:

Student name
Roll number
Marks
Grade

(C & C++ both)

✍️ Q2:

Write a program to input age & print:

You are eligible for vote

If age >= 18

✍️ Q3:

Make a flowchart to enter 2 numbers and display their sum.

✅ Mini Quiz

1) Which of these is a valid variable?

a) 2num
b) _roll ✅
c) my-name

2) char stores?
a) Words
b) Decimal numbers
c) Single character ✅

🎯 Output practice task

Write a program to print this:

My name is Rahul
I am 20 years old
My grade is A

📘 Chapter 3: Input / Output (I/O)

(English + Hindi)

✅ What is Input?

English:
Input means taking information from the user.

Hindi:
Input का मतलब है यूज़र से जानकारी लेना।

✅ What is Output?

English:
Output means displaying information/results to the user.

Hindi:
Output का मतलब है यूज़र को जानकारी/परिणाम दिखाना।

✅ Input / Output in C

📌 Header File

#include <stdio.h>

📌 Output Function

printf("message");

📌 Input Function

scanf("%d", &variable);

📍 Example (C) — Input 2 Numbers & Print Sum

#include <stdio.h>

int main() {
    int a, b, sum;
    
    printf("Enter first number: ");
    scanf("%d", &a);
    
    printf("Enter second number: ");
    scanf("%d", &b);
    
    sum = a + b;
    
    printf("Sum = %d", sum);
    return 0;
}

✅ Input / Output in C++

📌 Header File

#include <iostream>
using namespace std;

📌 Output Function

cout << "message";

📌 Input Function

cin >> variable;

📍 Example (C++) — Input 2 Numbers & Print Sum

#include <iostream>
using namespace std;

int main() {
    int a, b, sum;

    cout << "Enter first number: ";
    cin >> a;

    cout << "Enter second number: ";
    cin >> b;

    sum = a + b;

    cout << "Sum = " << sum;
    return 0;
}

🧠 Flowchart: Input & Output

+---------+
|  Start  |
+---------+
     |
     v
+----------------+
| Take Input A,B |
+----------------+
     |
     v
+---------------+
| Calculate A+B |
+---------------+
     |
     v
+-------------+
| Display Sum |
+-------------+
     |
     v
+---------+
|  End    |
+---------+

🎯 Format Specifiers (C Language)

Data Type	Format Specifier	Example
int	`%d`	10
float	`%f`	20.5
char	`%c`	‘A’
string	`%s`	“Rahul”

📝 Practice Tasks

✅ Task-1

Take input: Name, Age, City
And print:

Hello <Name>, Age: <Age>, City: <City>

✅ Task-2

Write C & C++ program to input 3 numbers and print average.

✅ Task-3

Flowchart to enter marks and show pass/fail.
(Passing marks > 40)

✨ Mini MCQ Quiz

Which is input in C++?
a) printf
b) cout
c) cin ✅
%d is used for:
a) decimal number ✅
b) string
c) character

📘 Chapter-4: Operators (C & C++)

(English + Hindi + Programs + Practice)

✅ What is an Operator?

English:
Operators are symbols used to perform operations on values and variables.

Hindi:
Operators वे symbols होते हैं जिनका उपयोग गणना/कार्य करने के लिए किया जाता है।

✅ Types of Operators

Type	Meaning	Example
Arithmetic	Maths operations	`+ - * / %`
Relational	Comparison	`> < >= <= == !=`
Logical	True/False logic	`&&
Assignment	Assign value	`= += -= *= /=`
Increment / Decrement	Increase / Decrease	`++ --`
Conditional	Ternary operator	`?:`
Bitwise	Bit operations	`&

✨ 1) Arithmetic Operators (गणितीय ऑपरेटर)

Operator	Meaning	Example
`+`	Addition	`a + b`
`-`	Subtraction	`a - b`
`*`	Multiplication	`a * b`
`/`	Division	`a / b`
`%`	Modulus (Remainder)	`a % b`

📍 Example (C / C++ Same Logic)

int a = 10, b = 3;
printf("%d", a % b); // Output: 1

int a = 10, b = 3;
cout << a % b; // Output: 1

✨ 2) Relational Operators (तुलना करने वाले)

Operator	Meaning	Example
`==`	Equal to	`a == b`
`!=`	Not equal	`a != b`
`>`	Greater	`a > b`
`<`	Less	`a < b`
`>=`	Greater or equal	`a >= b`
`<=`	Less or equal	`a <= b`

✨ 3) Logical Operators (तर्क वाले)

Operator	Meaning	Example
`&&`	AND	`(a>5 && b<10)`
`		`
`!`	NOT	`!(a>b)`

✨ 4) Increment / Decrement

Operator	Meaning
`++`	Increase value by 1
`--`	Decrease value by 1

Example:

int x = 5;
x++; // 6

🧠 Flowchart: Operator Usage

Start
 ↓
Enter A, B
 ↓
Perform A+B
 ↓
Display Result
 ↓
End

✅ Example Program (C)

#include <stdio.h>
int main() {
    int a = 10, b = 3;
    
    printf("Addition = %d\n", a + b);
    printf("Subtraction = %d\n", a - b);
    printf("Multiplication = %d\n", a * b);
    printf("Division = %d\n", a / b);
    printf("Modulus = %d\n", a % b);
    
    return 0;
}

✅ Example Program (C++)

#include <iostream>
using namespace std;

int main() {
    int a = 10, b = 3;

    cout << "Addition = " << a + b << endl;
    cout << "Subtraction = " << a - b << endl;
    cout << "Multiplication = " << a * b << endl;
    cout << "Division = " << a / b << endl;
    cout << "Modulus = " << a % b << endl;

    return 0;
}

📝 Exercises / अभ्यास

1️⃣ Input two numbers and perform all arithmetic operations
2️⃣ Check if number > 18 (true/false)
3️⃣ Find remainder when number is divided by 5
4️⃣ Use ++ and — on a variable and print results
5️⃣ Write a flowchart for simple calculator

🎯 MCQ

% operator gives:
a) Division
b) Remainder ✅
c) Multiplication
== checks:
a) Equal ✅
b) Assignment
c) Address

📘 Chapter-5: Conditional Statements

✅ Why Conditions?

English:
Conditions allow a program to take decisions — run different code based on true/false.

Hindi:
Conditions से प्रोग्राम निर्णय लेता है — यानी स्थिति के अनुसार अलग-अलग कोड चलता है।

✅ Types of Conditional Statements

Statement	Meaning
`if`	Executes code if condition true
`if-else`	True → run one block, False → second block
`else if`	Multiple conditions
`switch`	Menu-based multi-choice

✨ if Statement

SYNTA X

if(condition) {
   // code
}

Example

Check if age ≥ 18

✅ C Program

#include <stdio.h>
int main() {
    int age;
    printf("Enter age: ");
    scanf("%d", &age);

    if(age >= 18) {
        printf("Eligible for vote");
    }
    return 0;
}

✅ C++ Program

#include <iostream>
using namespace std;

int main() {
    int age;
    cout << "Enter age: ";
    cin >> age;

    if(age >= 18) {
        cout << "Eligible for vote";
    }
    return 0;
}

✨ if-else Statement

Example

Check even or odd number

✅ C

#include <stdio.h>
int main() {
    int n;
    printf("Enter number: ");
    scanf("%d", &n);

    if(n % 2 == 0)
        printf("Even");
    else
        printf("Odd");

    return 0;
}

✅ C++

#include <iostream>
using namespace std;

int main() {
    int n;
    cout << "Enter number: ";
    cin >> n;

    if(n % 2 == 0)
        cout << "Even";
    else
        cout << "Odd";

    return 0;
}

✨ else if Ladder

Example — Student grade

Marks >= 90 → A  
Marks >= 75 → B  
Marks >= 50 → C  
Else → Fail

✅ C / C++

int marks;
cin >> marks;

if(marks >= 90)
    cout << "Grade A";
else if(marks >= 75)
    cout << "Grade B";
else if(marks >= 50)
    cout << "Grade C";
else
    cout << "Fail";

✨ switch Case

Used for menu/program options.

Example — Day number to name

int day;
cin >> day;

switch(day) {
    case 1: cout<<"Monday"; break;
    case 2: cout<<"Tuesday"; break;
    case 3: cout<<"Wednesday"; break;
    default: cout<<"Invalid";
}

🧠 Flowchart — if-else (Vote Eligibility)

Start
 ↓
Enter Age
 ↓
Age ≥ 18 ?
 → Yes: Print "Eligible"
 → No: Print "Not Eligible"
 ↓
End

📝 Practice Problems

1️⃣ Input marks and print Grade (A/B/C/Fail)
2️⃣ Check positive, negative, zero
3️⃣ Menu:

1 = English
2 = Hindi
3 = Exit

4️⃣ Check divisibility by 5 & 11
5️⃣ Student pass if >= 40 else fail

🎯 MCQ

if(x>10) means:
✔ true if x > 10
Which is multi-option?
✔ switch

📎 Tip

Use == for compare, not =
👉 if(a==5) ✅
👉 if(a=5) ❌

📘 Loops

✅ What is a Loop?

English:
A loop executes a block of code repeatedly until a condition becomes false.

Hindi:
Loop बार-बार कोड चलाता है जब तक condition false न हो जाए।

✅ Types of Loops

Loop	Meaning	Hindi
`for`	Known number of repetitions	निश्चित बार के लिए
`while`	Condition first, then loop	Condition पहले check
`do-while`	Runs at least once	पहले चलता है, फिर check

1️⃣ for Loop

Syntax

for(initialization; condition; increment) {
    // code
}

Example: Print 1 to 5

C

#include <stdio.h>
int main() {
    for(int i=1; i<=5; i++) {
        printf("%d\n", i);
    }
    return 0;
}

C++

#include <iostream>
using namespace std;

int main() {
    for(int i=1; i<=5; i++) {
        cout << i << endl;
    }
    return 0;
}

2️⃣ while Loop

Example: Print 1 to 5

C / C++

int i = 1;
while(i <= 5) {
    printf("%d\n", i);
    i++;
}

3️⃣ do-while Loop

Example: Print 1 to 5

int i = 1;
do {
    printf("%d\n", i);
    i++;
} while(i <= 5);

✅ Runs once even if condition false.

🧠 Flowchart: for Loop (1-5)

Start
 ↓
i = 1
 ↓
Is i <= 5?
 → Yes → Print i → i = i+1 → repeat
 → No → End

⭐ Common Loop Examples

💡 Sum of 1 to N

int n, sum=0;
cin >> n;
for(int i=1; i<=n; i++) {
    sum += i;
}
cout << sum;

💡 Print Multiplication Table

int n;
cin >> n;
for(int i=1; i<=10; i++) {
    cout << n << " x " << i << " = " << n*i << endl;
}

💡 Factorial of Number

int n, fact=1;
cin >> n;
for(int i=1; i<=n; i++) {
    fact *= i;
}
cout << fact;

⚠️ Infinite Loop

while(1) {
   // endless loop
}

🎯 Loop Uses in Real Life

Counting marks
Repeating menu in ATM
Printing bill items
Games: repeat turns

📝 Exercises

1️⃣ Print 1 to 100
2️⃣ Print all even numbers 1-50
3️⃣ Print table of 15
4️⃣ Display sum of digits of a number
5️⃣ Find factorial of a number
6️⃣ Print this pattern:

*  
* *  
* * *  
* * * *

❓ MCQ

1. Which loop runs at least once?
✔ do-while

2. for loop syntax order?
Initialization → Condition → Increment ✅

🧠 Tip

If you don’t know how many times to run → while
If you know count → for

✅ What is a Function?

English:
A function is a block of code that performs a specific task and can be reused.

Hindi:
Function कोड का एक भाग होता है जो एक काम करता है और उसे बार-बार इस्तेमाल किया जा सकता है।

✅ Why Functions? (क्यों ज़रूरी?)

Advantage	Explanation
Reusability	Same code used multiple times
Easy Debugging	Errors easy to fix
Cleaner Code	Code becomes organized
Team Work	Program divided into parts

Hindi:
Functions कोड को छोटा, साफ़ और समझने लायक बनाते हैं।

✅ Function Types

Type	C	C++	Meaning
Built-in	`printf()`, `scanf()`	`cout`, `cin`	Already defined
User Defined	Programmer creates	Programmer creates	Custom function

✅ Function Syntax

C

returnType functionName(parameters) {
    // code
}

C++

returnType functionName(parameters) {
    // code
}

✅ Example — Function Without Return, Without Parameter

C Program

#include <stdio.h>

void hello() {
    printf("Hello World");
}

int main() {
    hello();
    return 0;
}

C++ Program

#include <iostream>
using namespace std;

void hello() {
    cout << "Hello World";
}

int main() {
    hello();
    return 0;
}

✅ Example — Function With Return & Parameters

C

#include <stdio.h>

int add(int a, int b) {
    return a + b;
}

int main() {
    int result = add(5, 3);
    printf("Sum = %d", result);
    return 0;
}

C++

#include <iostream>
using namespace std;

int add(int a, int b) {
    return a + b;
}

int main() {
    cout << "Sum = " << add(5, 3);
    return 0;
}

✅ Flowchart — Function Call

Start
 ↓
Main Program
 ↓
Call Function
 ↓
Function Executes Task
 ↓
Return to Main
 ↓
End

✅ Function With Return, No Parameter

int getNumber() {
    return 10;
}

✅ Function No Return, With Parameters

void greet(string name) {
    cout << "Hello " << name;
}

✅ Real-life examples of functions

Real Life	Programming Example
Calculator button	add(), sub()
ATM menu	withdraw(), balanceCheck()
Mobile apps	login(), logout()

🧠 Important Notes

Term	Meaning
Parameter	Value received by function
Argument	Value passed during call
Return	Sends result back

🚀 Output Example

Hello World
Sum = 8

📝 Practice Questions

1️⃣ Write a function to find square of a number
2️⃣ Create a function that prints your name
3️⃣ Create a function to check even or odd
4️⃣ Make a function to find factorial
5️⃣ Make a calculator using 4 functions: add, subtract, multiply, divide

🎯 MCQ Test

Function that returns nothing
a) int
b) float
c) void ✅
Function parameters are written in
a) main()
b) function definition ✅
c) printf

🎓 Tip

If a task repeats → Use a Function

📘 What is an Array?

English:
An array is a collection of multiple values of the same data type stored in a single variable.

Hindi:
Array एक ऐसा variable है जिसमें एक ही प्रकार के कई मान (values) store किये जाते हैं।

✅ Why use Arrays? / Arrays क्यों?

Reason	English	Hindi
Saves memory	One variable stores many values	एक variable में कई values
Easy access	Index through values	Index द्वारा values मिलती हैं
Better management	Avoids many variables	कई variables बनाने की ज़रूरत नहीं

✅ Array Declaration

Syntax

dataType arrayName[size];

Example

int marks[5];

Means: 5 integers stored

✅ Initialize Array

C / C++

int marks[5] = {80, 75, 92, 60, 85};

✅ Access Array Elements

printf("%d", marks[0]);  // first element

Index starts from 0

Index	Value
0	80
1	75
2	92
3	60
4	85

🧠 Flowchart Logic — Print Array

Start
 ↓
Declare array
 ↓
Set i = 0
 ↓
i < size?
 → Yes: print value[i], i++
 → No: End

✅ Program: Print Array (C)

#include <stdio.h>
int main() {
    int marks[5] = {80, 75, 92, 60, 85};

    for(int i = 0; i < 5; i++) {
        printf("%d\n", marks[i]);
    }
    return 0;
}

✅ Program: Print Array (C++)

#include <iostream>
using namespace std;

int main() {
    int marks[5] = {80, 75, 92, 60, 85};

    for(int i = 0; i < 5; i++) {
        cout << marks[i] << endl;
    }
    return 0;
}

⭐ Input Array from User

C

int arr[5];
for(int i=0; i<5; i++) {
    scanf("%d", &arr[i]);
}

C++

int arr[5];
for(int i=0; i<5; i++) {
    cin >> arr[i];
}

🎯 Sum of Array Elements

int arr[5] = {1,2,3,4,5}, sum=0;

for(int i=0;i<5;i++){
    sum += arr[i];
}
cout << sum;

🧠 2D Array (Matrix)

C++ Example

int a[2][2] = {{1,2},{3,4}};
cout << a[1][1]; // 4

💡 Real-Life Use

Real world	Code
Student marks list	marks[]
Shopping cart	items[]
ATM pin digits	pin[]

📝 Exercises

1️⃣ Create array of 10 numbers & print
2️⃣ Find sum of 5 numbers
3️⃣ Find largest number in array
4️⃣ Input 5 marks and find average
5️⃣ Make 3×3 matrix & print values

🎯 MCQ

Array index starts from?
a) 1
b) 0 ✅
c) -1
int a[5] stores:
a) 5 integers ✅
b) 4 integers
c) Infinite integers

🔥 Tip

Use array when you need same type of data stored in group

📘 Pointers & References

✅ What is a Pointer?

English:
A pointer is a variable that stores the memory address of another variable.

Hindi:
Pointer एक variable है जो किसी दूसरे variable का memory address store करता है।

✅ Why use pointers?

Reason	English	Hindi
Direct memory access	Faster performance	Memory पर direct काम
Pass by reference	Efficient function calls	Function में data copy नहीं
Dynamic memory	malloc / new	Memory control

✅ Declaring Pointer

Syntax

int *ptr;

Example

int a = 10;
int *p = &a;

Symbol	Meaning
`*`	Pointer variable
`&`	Address operator

✅ Memory Concept Diagram

Variable: a = 10
Address : 1001

Pointer p = &a   →  stores address 1001
*p gives value   →  10

✅ C Program: Pointer

#include <stdio.h>
int main() {
    int a = 10;
    int *p = &a;

    printf("Value = %d\n", a);
    printf("Address = %p\n", p);
    printf("Value using pointer = %d\n", *p);
    return 0;
}

✅ Pointer in C++

#include <iostream>
using namespace std;

int main() {
    int a = 10;
    int *p = &a;

    cout << "Value = " << a << endl;
    cout << "Address = " << p << endl;
    cout << "Value using pointer = " << *p;
    return 0;
}

🌟 Pointer & Function

void change(int *x){
    *x = 50;
}

int main(){
    int a = 10;
    change(&a);
    cout << a; // Output: 50
}

✅ What is Reference? (C++ Only)

English:
Reference is an alias (another name) for a variable.

Hindi:
Reference variable किसी variable का दूसरा नाम होता है।

Syntax

int a = 10;
int &r = a;

Now r and a both refer to same memory.

✅ Example: Reference

int a = 10;
int &b = a;

b = 20;
cout << a; // Output: 20

⭐ Pointer vs Reference

Feature	Pointer	Reference
Syntax	`int *p`	`int &r`
Null allowed?	Yes	No
Reassign later?	Yes	No
Used in C?	✅	❌
Used in C++?	✅	✅

🧠 Flowchart – Pointer Concept

Start
 ↓
Declare variable a
 ↓
Pointer p = &a
 ↓
Use *p to access value
 ↓
End

📝 Practice Tasks

1️⃣ Declare int pointer & print address and value
2️⃣ Create pointer to float
3️⃣ Swap 2 numbers using pointers
4️⃣ Write C++ program using reference
5️⃣ Pointer arithmetic: increment pointer

🎯 MCQ Test

Question	Answer
Pointer stores?	Address ✅
`&` means?	Address of variable ✅
Reference in C?	No ❌

✨ Tip

Pointers = Memory boss
References = Alias / shortcut name

📘 What is a String?

English:
A string is a sequence of characters.

Hindi:
String characters (letters, digits, symbols) का समूह होता है।

Examples: "Hello", "India", "IISDVT2025"

✅ Strings in C

🔹 C strings are character arrays

char name[20] = "Rahul";

char name[20] = {'R','a','h','u','l','\0'};

\0 = Null character (string terminator)

✅ Input & Output in C

#include <stdio.h>

int main() {
    char name[30];
    printf("Enter your name: ");
    scanf("%s", name);    // stops at space

    printf("Hello %s", name);
    return 0;
}

✅ Accept string with spaces (C)

gets(name);   // NOT recommended (unsafe)
fgets(name, 30, stdin); // best method

🔧 Common String Functions (C)

Function	Meaning
`strlen(s)`	length of string
`strcpy(a,b)`	copy b → a
`strcat(a,b)`	append b to a
`strcmp(a,b)`	compare strings

Example:

char s1[20]="Hello", s2[20]="World";
strcat(s1,s2); // s1 = HelloWorld

✅ Strings in C++

C++ provides string class (easier than C)

#include <iostream>
#include <string>
using namespace std;

int main() {
    string name;
    cout << "Enter name: ";
    getline(cin, name);

    cout << "Welcome " << name;
}

⭐ Common string functions in C++

name.length();
name.size();
name.append(" India");
name.compare(other);
name.substr(0,3);

Example:

string s="Hello";
cout << s.substr(0,2); // He

🧠 Memory View

char name[6] = "India";

I n d i a \0
0 1 2 3 4 5

🧠 Flowchart — String Input & Print

Start
 ↓
Declare string
 ↓
Input name
 ↓
Display "Hello <name>"
 ↓
End

📝 Practice Exercises

1️⃣ Take name and print

Hello <name>, welcome!

2️⃣ Input first & last name → join & print full name

3️⃣ Count characters of a string

4️⃣ Reverse string (no built-in)

5️⃣ Check palindrome
(Example: madam, level)

🎯 MCQ

Question	Answer
String ends with?	`\0` ✅
C++ string input with spaces?	`getline()` ✅
C string type?	char array ✅

⚠️ Tip

C uses char array
C++ uses string class (best)
Always use fgets instead of gets

📘 What are Structures & Classes?

✅ Structure (C & C++)

English:
Structure is a user-defined datatype used to group different data types.

Hindi:
Structure ऐसा datatype है जिसमें अलग-अलग प्रकार के values को एक साथ store किया जाता है।

Example uses: student record, employee data, bank record

✅ Class (C++ Only)

English:
Class is an advanced data structure that contains data + functions (OOP concept).

Hindi:
Class एक advanced structure है जिसमें data और उस data पर काम करने वाले functions दोनों होते हैं।

🆚 Structure vs Class — Difference Table

Feature	Structure	Class
Language	C & C++	Only C++
Purpose	Group data	Data + Functions (OOP)
Access specifier default	Public	Private
OOP support	❌ No	✅ Yes
Security	Low	High (Data hiding)

Hindi Note:
Class में security ज्यादा होती है क्योंकि data hide किया जा सकता है।

✅ Syntax — Structure in C

#include <stdio.h>

struct Student {
    int roll;
    char name[20];
    float marks;
};

int main() {
    struct Student s1 = {101, "Rahul", 88.5};
    printf("%d %s %.2f", s1.roll, s1.name, s1.marks);
}

✅ Syntax — Structure in C++

#include <iostream>
using namespace std;

struct Student {
    int roll;
    string name;
    float marks;
};

int main() {
    Student s1 = {101, "Rahul", 88.5};
    cout << s1.roll << " " << s1.name << " " << s1.marks;
}

✅ Class in C++ — Example

#include <iostream>
using namespace std;

class Student {
private:
    int roll;
    float marks;

public:
    void setData(int r, float m) {
        roll = r;
        marks = m;
    }

    void display() {
        cout << "Roll: " << roll << " Marks: " << marks;
    }
};

int main() {
    Student s;
    s.setData(101, 90.5);
    s.display();
}

Key Concepts Used:

private data → hidden
public functions → access data

🧠 Flowchart — Class Use

Start
 ↓
Create Object
 ↓
Call setData()
 ↓
Call display()
 ↓
End

🌟 Real Life Analogy

Real-Life	Programming
Student Form	Structure
Student with actions (study(), attend(), marks())	Class

📝 Practice Questions

1️⃣ Create structure Employee with name, id, salary
2️⃣ Take user input for 3 students & print
3️⃣ Create class Car with model, year, show() method
4️⃣ Compare structure & class (10 points)
5️⃣ Make class with input() & output() methods

🎯 Mini MCQ

Question	Answer
Class default access	private ✅
Structure stores?	Multiple data types ✅
OOP supported in structure?	❌

💡 Tip

Structure = data only
Class = data + functions (OOP)

After this chapter:
📕 Full PDF + Word File
🏁 Practice Sheets
✅ Viva Questions
🎯 Project Assignments
📂 Printable Notes Version

Just say yes/next 👇 and we continue.

📘 Chapter-12: Object-Oriented Programming (OOP) in C++

✅ What is OOP?

English:
OOP (Object-Oriented Programming) is a programming style based on objects that contain data & functions.

Hindi:
OOP एक प्रोग्रामिंग तरीका है जिसमें प्रोग्राम objects के रूप में बनाया जाता है — जिनमें data और functions दोनों होते हैं।

🎯 4 Pillars of OOP

Concept	Meaning	Hindi
Encapsulation	Bundle data + functions	Data को सुरक्षित बांधना
Inheritance	Derive new class from old	गुणों का विरासत में मिलना
Polymorphism	One name, many forms	एक नाम, कई रूप
Abstraction	Hide complexity	केवल ज़रूरी चीजें दिखाना

✅ 1. Encapsulation

Data + functions inside a class
Data security using private members

Example

#include<iostream>
using namespace std;

class Student {
private:
    int marks;

public:
    void setMarks(int m) { marks = m; }
    int getMarks() { return marks; }
};

int main() {
    Student s;
    s.setMarks(90);
    cout << s.getMarks();
}

✅ 2. Inheritance

Parent → Child

Types of Inheritance

Single
Multi-level
Multiple
Hierarchical
Hybrid

Example (Single Inheritance)

class A {
public:
    void showA(){ cout<<"Class A\n"; }
};

class B : public A {
public:
    void showB(){ cout<<"Class B"; }
};

int main(){
    B obj;
    obj.showA();
    obj.showB();
}

✅ 3. Polymorphism

Same function name → different behavior

Types

Compile-time (Function Overloading)
Run-time (Function Overriding)

Function Overloading

class Test {
public:
    void sum(int a,int b){ cout<<a+b; }
    void sum(float a,float b){ cout<<a+b; }
};

Function Overriding

class A { public: void show(){ cout<<"A"; } };
class B: public A { public: void show(){ cout<<"B"; } };

✅ 4. Abstraction

Show only necessary details
Hide complex details

Example: ATM
You see options → internal code hidden

Example

class Car {
public:
    void startEngine(){ cout<<"Engine Started"; }
private:
    void fuelPump(){ }
};

🌟 Object and Class Example

class Student {
public:
    string name;
    void intro() { cout << "My name is " << name; }
};

int main() {
    Student s;
    s.name = "Amit";
    s.intro();
}

🧠 OOP Real-Life Example

Real World	OOP
Car	Class
Specific car	Object
Car functions	Methods
Keys lock car	Encapsulation
Driver uses only steering	Abstraction

📊 Flowchart — OOP Object Creation

Start
 ↓
Define Class
 ↓
Create Object
 ↓
Call Methods
 ↓
End

🎯 Exercises

1️⃣ Create a class Bank with deposit & withdraw
2️⃣ Create Teacher (base) & SubjectTeacher (derived)
3️⃣ Function overloading: sum of 2 & 3 numbers
4️⃣ Create class Laptop → brand, price, show()
5️⃣ Create ATM program using OOP concepts

🧪 MCQ Quiz

Question	Answer
OOP is based on?	Objects ✅
Default access in class	Private ✅
Inheritance meaning	properties transfer ✅
Encapsulation means	data hiding ✅