# Introduction to class and object in C#

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` :
```cs
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](https://vishalpawarr.hashnode.dev/access-modifiers-in-c-sharp).

> 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 :

```cs
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](https://vishalpawarr.hashnode.dev/constructor-in-csharp).

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