## **1. Define a Basic Class**

**Problem:**
Create a class `Car` with attributes `brand`, `model`, and `year`.
Add a method `start_engine()` that prints a message like:
`"The 2022 Tesla Model S engine has started."`

**Explanation:**
Introduces the concept of defining a class, using the constructor (`__init__`), and creating methods that use instance data.

**Sample Input:**

```
car1 = Car("Tesla", "Model S", 2022)
car1.start_engine()

```

**Sample Output:**

```
The 2022 Tesla Model S engine has started.

```

***

## **2. Class Representing a Movie**

**Problem:**
Create a class `Movie` with attributes `title`, `director`, and `rating`.
Add a method `describe()` that prints details like:
`"Inception directed by Christopher Nolan has a rating of 9.0."`

**Explanation:**
Shows how to represent real-world entities and display their information through methods.

**Sample Input:**

```
movie1 = Movie("Inception", "Christopher Nolan", 9.0)
movie1.describe()

```

**Sample Output:**

```
Inception directed by Christopher Nolan has a rating of 9.0.

```

***

## **3. Shopping Cart with Total Calculation**

**Problem:**
Create a class `ShoppingCart` that stores items and prices.
Add methods:

* `add_item(name, price)`
* `total()` — returns the total price

**Explanation:**
Teaches how to store multiple data (lists or dictionaries) inside objects and operate on them using methods.

**Sample Input:**

```
cart = ShoppingCart()
cart.add_item("Book", 250)
cart.add_item("Pen", 30)
cart.total()

```

**Sample Output:**

```
Total: ₹280

```

***

## **4. Track Employee Bonuses**

**Problem:**
Create a class `Employee` with `name` and `salary`.
Add a method `apply_bonus(percent)` that increases the salary by a percentage.

**Explanation:**
Practices modifying attributes and applying formulas within methods.

**Sample Input:**

```
emp = Employee("Aman", 50000)
emp.apply_bonus(10)

```

**Sample Output:**

```
Bonus applied. New salary: ₹55000.0

```

***

## **5. Temperature Converter**

**Problem:**
Create a class `Temperature` with a Celsius value.
Add methods:

* `to_fahrenheit()`
* `to_kelvin()`

**Explanation:**
Shows conversion logic and returning computed values via methods.

**Sample Input:**

```
t = Temperature(25)
print(t.to_fahrenheit())
print(t.to_kelvin())

```

**Sample Output:**

```
77.0
298.15

```

***

## **6. Simple Library System**

**Problem:**
Create a class `Book` with `title`, `author`, and `is_available=True`.
Add:

* `borrow()` → makes it unavailable
* `return_book()` → makes it available again

**Explanation:**
Demonstrates state changes using boolean attributes.

**Sample Input:**

```
book1 = Book("Harry Potter", "J.K. Rowling")
book1.borrow()
book1.return_book()

```

**Sample Output:**

```
Book borrowed successfully.
Book returned successfully.

```

***

## **7. Simple Bank Account with Validation**

**Problem:**
Create a class `BankAccount` with `holder_name` and `balance=0`.
Add:

* `deposit(amount)`
* `withdraw(amount)` (only if balance ≥ amount)
* `display_balance()`

**Explanation:**
Shows conditional logic and secure data updates within an object.

**Sample Input:**

```
acc = BankAccount("Ravi")
acc.deposit(1000)
acc.withdraw(300)
acc.display_balance()

```

**Sample Output:**

```
Deposited ₹1000
Withdrew ₹300
Current balance: ₹700

```

***

## **8. Class for Student Marks**

**Problem:**
Create a class `Student` that stores `name` and three subject marks.
Add:

* `average()` → returns average marks
* `grade()` → returns grade based on average

**Explanation:**
Combines arithmetic and conditional logic with OOP.

**Sample Input:**

```
student1 = Student("Anita", 75, 85, 90)
print(student1.average())
print(student1.grade())

```

**Sample Output:**

```
83.33
A

```

***

## **9. Car Mileage Tracker**

**Problem:**
Create a class `MileageTracker` with `distance` and `fuel_used`.
Add a method `calculate_mileage()` that returns distance ÷ fuel.
If fuel is 0, handle it gracefully.

**Explanation:**
Shows how to handle invalid data or prevent runtime errors inside a method.

**Sample Input:**

```
trip = MileageTracker(400, 20)
print(trip.calculate_mileage())

```

**Sample Output:**

```
Mileage: 20.0 km/l

```

***

## **10. Product Discount System**

**Problem:**
Create a class `Product` with `name`, `price`, and `category`.
Add:

* `apply_discount(percent)` — reduces price by that percent
* `display_info()` — prints product info

**Explanation:**
Focuses on modifying and displaying data in an organized way.

**Sample Input:**

```
p = Product("Laptop", 60000, "Electronics")
p.apply_discount(10)
p.display_info()

```

**Sample Output:**

```
Product: Laptop | Category: Electronics | Price after discount: ₹54000.0

```

"The 2022 Tesla Model S engine has started."

Introduces the concept of defining a class, using the constructor (

), and creating methods that use instance data.

car1 = Car("Tesla", "Model S", 2022)
car1.start_engine()


The 2022 Tesla Model S engine has started.


"Inception directed by Christopher Nolan has a rating of 9.0."

Shows how to represent real-world entities and display their information through methods.

movie1 = Movie("Inception", "Christopher Nolan", 9.0)
movie1.describe()


Inception directed by Christopher Nolan has a rating of 9.0.


Teaches how to store multiple data (lists or dictionaries) inside objects and operate on them using methods.

cart = ShoppingCart()
cart.add_item("Book", 250)
cart.add_item("Pen", 30)
cart.total()


 that increases the salary by a percentage.

Practices modifying attributes and applying formulas within methods.

emp = Employee("Aman", 50000)
emp.apply_bonus(10)


Shows conversion logic and returning computed values via methods.

t = Temperature(25)
print(t.to_fahrenheit())
print(t.to_kelvin())


Demonstrates state changes using boolean attributes.

book1 = Book("Harry Potter", "J.K. Rowling")
book1.borrow()
book1.return_book()


Book borrowed successfully.
Book returned successfully.


Shows conditional logic and secure data updates within an object.

acc = BankAccount("Ravi")
acc.deposit(1000)
acc.withdraw(300)
acc.display_balance()


Deposited ₹1000
Withdrew ₹300
Current balance: ₹700


Combines arithmetic and conditional logic with OOP.

student1 = Student("Anita", 75, 85, 90)
print(student1.average())
print(student1.grade())


Shows how to handle invalid data or prevent runtime errors inside a method.

trip = MileageTracker(400, 20)
print(trip.calculate_mileage())


Focuses on modifying and displaying data in an organized way.

p = Product("Laptop", 60000, "Electronics")
p.apply_discount(10)
p.display_info()


Product: Laptop | Category: Electronics | Price after discount: ₹54000.0
