Classes and Objects in C#

A class is a data structure in C# that combines data variables and functions into a single unit. Instances of the class are known as objects. While a class is just a blueprint, the object is an actual instantiation of the class and contains data. The different operations are performed on the object.

Class Definition

A new class requires a class definition. It starts with the class keyword and contains the class name. It also includes the attributes and modifiers of the class as well as its interfaces. Then the class body is provided within curly braces.

The syntax of a class definition is given as follows:

AccessSpecifier class NameOfClass
{
    // Member variables
    // Member functions
}

In the above syntax, AccessSpecifier provides the access specifier for the class. Then the keyword class is used which is followed by the NameOfClass. Then the class body is provided.

Object Definition

An object is a dynamically created instance of the class. It is created at runtime so it can also be called a runtime entity. All the members of the class can be accessed using the object.

The object definition starts with the class name followed by the object name. Then the new operator is used to create the object.

The syntax of the object definition is given as follows

NameOfClass NameOfObject = new NameOfClass();

In the above syntax, NameOfClass is the class name followed by the NameOfObject which is the object name.

A program that demonstrates class definition and object definition is given as follows:

Source Code: Program that demonstrates class definition and object definition in C#

using System;
namespace ClassDemo
{
  class Sum
  {
    private int x;
    private int y;
    public void setVal(int val1, int val2)
    {
        x = val1;
        y = val2;
    }
    public int getSum()
    {
        return x + y;
    }
   }
   class Test
   {
     static void Main(string[] args)
     {
        Sum s = new Sum();   
        s.setVal(3,14);
        Console.WriteLine("Sum of 3 and 14 is: {0}" , s.getSum());
     }
   }
}

The output of the above program is given as follows:

Sum of 3 and 14 is: 17

Static Variables in Class

Static variables in a class have only one instance even if there are multiple objects of the class. Because of this reason, static variables can be used to define constants. Static variables can be initialized inside the class definition or outside it using the static keyword.

A program that demonstrates static variables is given as follows:

Source Code: Program that demonstrates static variables in C#

using System;
namespace StaticVariableDemo
{
  class StaticVariable
  {
     public static int count;
     public StaticVariable()
     {
        count++;
     }
     public int getCount()
     {
        return count;
     }
  }
  class Test
  {
     static void Main(string[] args)
     {
        StaticVariable s1 = new StaticVariable();
        StaticVariable s2 = new StaticVariable();
        StaticVariable s3 = new StaticVariable();
        Console.WriteLine("Value of count for s1: {0}", s1.getCount());
        Console.WriteLine("Value of count for s2: {0}", s2.getCount());
        Console.WriteLine("Value of count for s3: {0}", s3.getCount());
     }
  }
}

The output of the above program is as follows:

Value of count for s1: 3
Value of count for s2: 3
Value of count for s3: 3

Static Function in Class

A member function in a class can also be declared as static using the static keyword. This function can access only static variables. It can also exist before any object of the class is created.

A program that demonstrates static function in class is given as follows:

Source Code: Program that demonstrates static function in C#

using System;
namespace StaticFunctionDemo
{
  class StaticDemo
  {
     public static int count = 5;
     public StaticDemo()
     {
        Console.WriteLine("Static Demo");
     }
     public static int getCount()
     {
        count++;
        return count;
     }
  }
  class Test
  {
     static void Main(string[] args)
     {
        Console.WriteLine("Value of count: {0}", StaticDemo.getCount());        
     }
  }
}

The output of the above program is as follows:

Value of count: 6