Whenever we are dealing with the OOPS concepts we are generally using the class and object.

What is class?

The class and objects are the blueprint or prototype. The class can be created for the entity which has states and behaviors. The entity may be a living or non-living thing.

Declaring the class :

AccessModifiers class ClassName
{
    // fields also known as variables

    // functions also known as methods
}

• The class will always have access modifiers to control the visibility of the class. To learn more about the access modifiers please check my blog on access modifiers.

Note: If we are not writing the access modifiers explicitly then the class will by default internal as access modifier.

• The classes are declared using the class keyword.

• The class will have the name and body the body of the class is surrounded using the { }.

Example :

namespace Demo
{
    class Add
    {
        int a = 10;
        int b = 20;
        public int sum;

        public void Sum()
        {
            sum = a + b;
        }
    }
    class Program
    {
        public static void Main()
        {
            Add add = new Add();

            add.Sum();
            Console.WriteLine($"The sum of a and b : {add.sum}");
        }

    }
}
/*
Output :
The sum of a and b: 30
*/

Explanation :

• namespace is a way of organizing the code and namespace also helps in avoiding the naming collision of the class.

• The access modifiers for the above class is internal because we didn't mention it explicitly.

• The class Add has variables like a, b, and sum. The Add class also has a method named Sum which takes above both values from a and b using the operator + performs the addition operation and store the value returned value inside the sum variable.

Note: In C# the execution of the program from Main() only.

• To access the variables and methods of the different classes we need to create the object of that class.

• To create the object of the class we use the new keyword.

Note: The objects created using the new keyword are stored inside the heap area.

• Whenever we create the object of the class the constructor of that class gets called.

Note: Each and every class has will have a constructor of its own even if we didn't write the constructor explicitly. To learn more about Constructor please check my blog on constructor.

• By using the object reference we can call the methods and variable and perform the required operation.