Objects and Classes in C++

1. Objects and Classes

1.1. A Simple Class

A class is a user-defined data type in C++ that can have both variables (data members) and functions (member functions).

class Car {
  public:
    string brand;
    int year;
 
    void start() {
        cout << "Car started!" << endl;
    }
};

1.2. Classes and Objects

An object is an instance of a class. You can create objects of a class using the class name.

Car myCar;
myCar.brand = "Toyota";
myCar.year = 2021;
myCar.start();

1.3. Specifying a Class

A class is defined using the class keyword. By default, all members are private. You can make them accessible using the public keyword.

class Box {
  private:
    double length;
  public:
    void setLength(double len) {
        length = len;
    }
 
    double getLength() {
        return length;
    }
};

1.4. Using a Class

Once a class is defined, you can create objects and use its members.

Box box1;
box1.setLength(10.0);
cout << "Length: " << box1.getLength();

1.5. C++ Objects as Physical Objects

Objects can represent physical entities in the real world. For example, a Car class could represent an actual car.

class Car {
  public:
    string model;
    double speed;
    void accelerate() {
        speed += 10;
    }
};

1.6. C++ Objects as Data Types

Objects can also represent more abstract data types. For example, an object of class Vector could represent a mathematical vector.

2. Constructors

Constructors are special functions that are automatically called when an object is created. They initialize the object's data members.

class Box {
  public:
    double length;
    Box(double len) {
        length = len;
    }
};

Example:

Box box1(10.0);
cout << "Length: " << box1.length;

3. Objects as Function Arguments

You can pass objects as arguments to functions.

void printBox(Box box) {
    cout << "Box length: " << box.length << endl;
}

3.1. Returning Objects from Functions

A function can return an object.

Box getBox(double len) {
    Box b(len);
    return b;
}

Arrays in C++

1. Array Fundamentals

An array is a collection of elements of the same data type stored in contiguous memory locations.

int numbers[5] = {1, 2, 3, 4, 5};

1.1. Defining an Array

An array is defined with a type, name, and size.

int arr[10];

1.2. Accessing Array Elements

You can access array elements using the index.

cout << arr[0];  // First element

1.3. Initializing Arrays

You can initialize arrays during declaration.

int arr[5] = {10, 20, 30, 40, 50};

1.4. Multidimensional Arrays

Arrays can have more than one dimension.

int matrix[3][3] = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};

2. Passing Arrays to Functions

You can pass arrays as arguments to functions.

void printArray(int arr[], int size) {
    for (int i = 0; i < size; i++) {
        cout << arr[i] << " ";
    }
}

3. Array of Objects

You can also create an array of objects.

class Student {
  public:
    string name;
    int age;
};
 
Student students[3] = {{"John", 20}, {"Anna", 22}, {"Mike", 21}};

4. Strings in C++

4.1. String Variables

Strings in C++ can be defined using character arrays or the string class.

string name = "John";

4.2. Avoiding Buffer Overflow

Buffer overflow occurs when the program writes data beyond the bounds of a fixed-size buffer (e.g., a character array).

char name[5];
strcpy(name, "Hello"); // Buffer overflow

4.3. String Constants

A string constant is a sequence of characters enclosed in double quotes.

const char* greeting = "Hello, World!";

5. Array of Strings

An array of strings is an array where each element is a string.

string colors[3] = {"Red", "Green", "Blue"};

5.1. Strings as Class Members

A string can be a member of a class.

class Person {
  public:
    string name;
    Person(string n) {
        name = n;
    }
};

5.2. Standard C++ String Class

C++ provides the string class, which makes working with strings easier compared to character arrays.

string str1 = "Hello";
string str2 = "World";
string result = str1 + " " + str2; // Concatenation