The following code explains the Destructors in C#.
Destructors begin with ~ symbol followed by class name.
There should not be any parameters in the brackets.

Syntax:

class A
    {
        ~A()
        {
           code;
        }
    }

Example:

using System;
using System.Text;

namespace forgetCode
{

    class A
    {
        ~A()
        {
            Console.WriteLine("Destruct instance of A");
        }
    }
    class B
    {
        object Ref;
        public B(object o)
        {
            Ref = o;
        }
        ~B()
        {
            Console.WriteLine("Destruct instance of B");
        }
    }


    class program
    {        
        public static void Main()
        {

            B b = new B(new A());
            b = null;
            GC.Collect();
            GC.WaitForPendingFinalizers();
        }
    }
}

Output:

Destruct instance of B
Destruct instance of A

or

Destruct instance of A
Destruct instance of B

The output could be either because the language imposes no constraints on the order in which objects are garbage collected.