Class

Class is a user-defined blueprint from which objects are created. Basically, a class combines the fields(variables) and methods into a single unit. In C#, classes support advance object oriented programming concepts like inheritance, abstraction etc. Everything in C# is associated with classes and objects, along with its attributes and methods.

Console.WriteLine("CodersCapsule") - Console is a class, WriteLine is a method which has a string parameter.
Convert.ToInt32("56") - Convert is a class, ToInt32 is a method which has a string parameter.
Console.ReadLine() - Console is a class, ReadLine is a method which don't have any parameter.
Math.Pow(5,6) - Math is a class, Pow is a method which has 2 double parameters.

NOTE
The main method what we studied since methods or functions topic is present inside a class called program. We can create our own class by going outside class program, directly inside namespace.


Before entering coding part of Class, we need to be clear with concept called Access Modifiers. Access Modifiers are keywords that define the accessibility of a member, class or datatype in a program. These are mainly used to restrict unwanted data manipulation by external programs or classes. There are 4 access modifiers present in C#, let us discuss each with its description.

Public - Accessible everywhere.
Private - Accessible within the same class.
Protected - Accessible within its child class(we'll learn more about this in Inheritance chapter).
Internal - Accessible within same project(we'll learn more about this in Dynamic Link Library(DLL) chapter).


CODE

EG 1 . Creating Rectangle class with fields and variables

class Program {
    static void Main() {

    }
}
//Creating class called Rectangle with its fields and methods.
class Rectangle {
    //In order to access fields and methods outside class, we need to use Public keyword before it.
    public double length, width, height;
    public double Area() {
        return length * width;
    }
    public double Perimeter() {
        return 2 * (length+width);
    }
    public double Volume() {
        return Area() * height;
    }
}

CODE EXPLANATION
Creating a class called Rectangle and loading that with some sensible fields and methods. If we compile above program nothing will be printed out since we haven't written anything inside main method. It doesn't matter how many classes we are creating, system will directly go inside main method inside program class and execcute whatever code we written inside because still that is our entry point.


EG 2 . Creating Class called car with fields and variables

class Program {
    static void Main() {

    }
}
class Car {
    public string color;
    public int weight, numberOfSeats;
    public void Drive() {
        Console.WriteLine("Start Driving");
    }
    public double CarryingLoadCapacity() {
        return (numberOfSeats*65)+30; //65 is the average weight of a person in kg, 30kg is for extra load for accessories,fuel etc.
    }
}

CODE EXPLANATION
Creating a class called Car and loading that with some sensible fields and methods. If we compile above program, here also nothing will be printed out since we haven't written anything inside main method. Not only the above mentioned fields and methods we can load classes with n number of sensible fields and methods.


Exercises
1. Create a class called MusicalInstruments with fields and methods.
2. Create a class called Circle with fields and methods.
3. Create a class called Triangle with fields and methods.


(Click Here, For more exercises)