Classes and Objects in CPP

---

Overview of Classes and Objects in C++

In C++, Classes are user-defined data types that serve as blueprints for creating Objects. They encapsulate data (member variables) and functions (member methods) that operate on that data into a single unit. This concept is fundamental to Object-Oriented Programming (OOP) and promotes code reusability, organization, and modularity.

An Object is an instance of a class. When a class is defined, no memory is allocated; memory is only allocated when an object of that class is created. Objects allow us to interact with the data and functions defined within the class.

---

1. Student Information

This program defines a class named student with public member variables: name, branch, subject (all strings), and result (float). It then creates two objects, s1 and s2, of the student class. For each student object, it assigns specific values to their respective member variables and then prints these details to the console, demonstrating how to access and display object properties.

Algorithm:

1. Define a student class with public members: name (string), branch (string), subject (string), result (float).
2. Declare two student objects, s1 and s2.
3. Assign values to s1's name, branch, subject, and result.
4. Print s1's details.
5. Assign values to s2's name, branch, subject, and result.
6. Print s2's details.

Output: student 1 Ninad Phatak Mechanical C++ 8.6 student 2 Atharv Jamali ENTC Mathematics 7

---

2. Car Details

This program defines a Car class with public member variables: brand, model (strings), year, and price (integers). The main function declares three Car objects: c1, c2, and c3. For each car, the program prompts the user to enter details such as brand, model, year, and price using standard input. After collecting all inputs, it displays the details of each car, demonstrating user input handling and object data storage.

Algorithm:

1. Define a Car class with public members: brand (string), model (string), year (int), price (int).
2. Declare three Car objects: c1, c2, c3.
3. For each car object (c1, c2, c3): a. Prompt the user to enter brand, model, year, and price. b. Read input values into the respective object's members.
4. Print a header "Car Details".
5. For each car object (c1, c2, c3): a. Print the car number (e.g., "Car 1:"). b. Print its brand, model, year, and price.

Output: Enter details for Car 1: Brand: BMW Model: X3 Year: 2022 Price: 1000000

Enter details for Car 2: Brand: Mazda Model: Miata Year: 1998 Price: 3000000

Enter details for Car 3: Brand: Toyota Model: Corolla Year: 2002 Price: 2000000 Car DetailsCar 1:Brand: BMWModel: X3Year: 2022Price: $1000000 Car 2:Brand: MazdaModel: MiataYear: 1998Price: $3000000 Car 3:Brand: ToyotaModel: CorollaYear: 2002Price: $2000000

---

3. Rectangle Area

This program defines a Rectangle class with private member variables length and width. It includes a constructor Rectangle(int l, int w) to initialize these dimensions when an object is created. The class also has two public methods: square() which returns true if the rectangle is a square (length equals width), and area() which calculates and returns the area. The main function takes user input for length and width, creates a Rectangle object, and then determines if it's a square or a rectangle before printing its calculated area.

Algorithm:

1. Define a Rectangle class with private members length and width.
2. Implement a constructor Rectangle(int l, int w) to initialize length and width.
3. Implement a public method bool square() that returns true if length == width, false otherwise.
4. Implement a public method double area() that returns length * width.
5. In main(): a. Declare length and width variables. b. Prompt the user to enter length and width. c. Read length and width. d. Create a Rectangle object r using the input length and width. e. Check if r.square() is true; if so, print "This is a square.", else print "This is a rectangle.". f. Print "Area: " followed by r.area().

Output: Enter length: 4 Enter width: 4 This is a square. Area: 16

Enter length: 2 Enter width: 3 This is a rectangle. Area: 6

---

4. Simple Calculator

This program implements a Calculator class to perform basic arithmetic operations. The class has private member variables x and y for the two numbers, initialized using a constructor Calculator(double a, double b). It provides public methods for add(), subtract(), multiply(), and divide(). The divide() method includes error handling for division by zero. The main function takes two numbers as input from the user, creates a Calculator object, and then displays the results of all four operations.

Algorithm:

1. Define a Calculator class with private members x and y (doubles).
2. Implement a constructor Calculator(double a, double b) to initialize x and y.
3. Implement public methods:
   • double add(): returns x + y.
   • double subtract(): returns x - y.
   • double multiply(): returns x * y.
   • double divide(): returns x / y if y != 0, otherwise prints an error and returns 0.
4. In main(): a. Declare a and b variables (doubles). b. Prompt the user to enter two numbers. c. Read a and b. d. Create a Calculator object calc using a and b. e. Print "Addition: " followed by calc.add(). f. Print "Subtraction: " followed by calc.subtract(). g. Print "Multiplication: " followed by calc.multiply(). h. Print "Division: " followed by calc.divide().

Output: Enter two numbers: 5 3 Addition: 8 Subtraction: 2 Multiplication: 15 Division: 1.66667

---

5. Volume of a cube with method inside class

This program defines a Cube class to calculate the volume of a cube. It has a private member variable side. The class includes a public input() method to prompt the user to enter the side length and a public volume() method that calculates the cube's volume (side * side * side). In the main function, a Cube object is created, its input() method is called to get the side, and then its volume() method is called to display the calculated volume.

Output: Enter side of cube: 4 Volume: 64

---

6. Volume of cube with method outside the class

This program also calculates the volume of a cube using a Cube class with a private side member. Similar to the previous example, it has an input() method to get the side length. However, the calculation of the volume is performed by a global function volume(Cube c) that takes a Cube object as an argument. The Cube class provides a k() method to return the side value, allowing the external volume function to access it. This demonstrates how a function outside the class can interact with object data through public member functions.

Output: Enter side of cube: 5.5 Volume: 166.375

---

7. Find Error

This program defines a cube class with public member variables height, width, and length, initialized with default values. It includes a volume() method that calculates the product of these dimensions. The main function creates a cube object, calls its volume() method, and then prints the height and the calculated volume. The "Find Error" in the title typically implies looking for logical or syntax errors, but in this case, the provided code runs correctly and produces the expected output based on the initial values. The "error" might be a conceptual prompt to understand how the code functions or to identify potential areas for improvement (e.g., making member variables private and using getters/setters).

Output: height 2volume 30