Object Creation And Difference Between Object And Reference Variable In C#

Box b1;//Reference variable,can not create memory
b1 is called a reference variable (not object)
now b1 is null
Box b2 = new Box();// object b2 of class BOX is instantiated and create memory on Heap
now b2 points box object
Box b3 = new Box();
b3.length = 10;
b3.width = 20;

b1 = b3; //an object is assigned to a reference variable

namespace ConsoleApplicationdemo {
    class Program {
        static void Main(string[] args) {
            Box b1; //Reference variable,not create memory
            Box b2 = new Box(); // object b2 of class BOX is instantiated and create memory on Heap
            Console.WriteLine("b2 object length:{0}", b2.length); //by default vale
            Console.WriteLine("b2 object width:{0}", b2.width); //by default vale
            Box b3 = new Box();
            b3.length = 10;
            b3.width = 20;
            Console.WriteLine("b3 object length:{0}", b3.length);
            Console.WriteLine("b3 object width:{0}", b3.width);
            b1 = b3; //an object is assigned to a reference variable
            //now reference variable works like an object
            //both b3 and b1 points to same memory location if any one updated then another one automatically updated
            Console.WriteLine("after assigning b3,the b1 object length:{0}", b1.length);
            Console.WriteLine("after assigning b3,the b1 object width:{0}", b1.width);
            ///////////////////////////modify b3
            b3.length = 45;
            b3.width = 55;
            Console.WriteLine("Modified b3 object length:{0}", b3.length);
            Console.WriteLine("Modified b3 object width:{0}", b3.width);
            Console.WriteLine("after modify b3,the b1 object length:{0}", b1.length);
            Console.WriteLine("after modify b3,the b1 object width:{0}", b1.width);
            ///////////////////////////modify b1
            b1.length = 70;
            b1.width = 80;
            Console.WriteLine("Modified b1 object length:{0}", b1.length);
            Console.WriteLine("Modified b1 object width:{0}", b1.width);
            Console.WriteLine("after modify b1,the b3 object length:{0}", b3.length);
            Console.WriteLine("after modify b1,the b3 object width:{0}", b3.width);
            Console.ReadKey();
        }
    }
    class Box {
        public int length;
        public int width;
        int height; // by default private ,any object of class cant access this data field
    }
}