using System;

class MyClass {
    public int Value;
}

class MainClass {
    public static void Main() {
        try {
            MyClass MyObject = new MyClass();
            MyObject = null;

            MyObject.Value = 123;

        } catch (NullReferenceException) {
            Console.WriteLine("Cannot reference a null object.");
        }
    }
}

           
          

   



using System;
public class MainClass {
    public static void Main() {

        string firstName = "J";
        string lastName = "R";
        string name = string.Format("{0} {1}", firstName, lastName);
        Console.WriteLine(name);
    }
}


          

   





using System;
public class MainClass {
    public static void Main() {
        string name = "Joe";
        Console.WriteLine(name.ToUpper());
    }
}

          

   
 

using System;


public class Starter {
    public static void Main() {
        Employee obj1 = new Employee(5678);
        Employee obj2 = (Employee)obj1.Clone();
        if (Employee.ReferenceEquals(obj1, obj2)) {
            Console.WriteLine("objects identical");
        } else {
            Console.WriteLine("objects not identical");
        }
    }
}
class Employee : ICloneable {
    public Employee(int id) {
        if ((id < 1000) || (id > 9999)) {
            throw new Exception(
                "Invalid Employee ID");
        }

    }
    public object Clone() {
        return MemberwiseClone();
    }
}

    

   

using System;
   
   
public class Name {
  public string firstName;
  public string lastName;
   
  public Name(string firstName, string lastName) {
    this.firstName = firstName;
    this.lastName = lastName;
  }
   
  public void Display() {
    Console.WriteLine("firstName = " + firstName);
    Console.WriteLine("lastName = " + lastName);
  }
   
  public static Name Copy(Name car) {
    return (Name) car.MemberwiseClone();
  }
}
   
   
class Test {
  public static void Main() {
    Name myName = new Name("T", "M");
    Name myOtherName = new Name("P", "B");
    Console.WriteLine("myName details:");
    myName.Display();
    Console.WriteLine("myOtherName details:");
    myOtherName.Display();
   
    // perform a memberwise clone of myName using the Name.Copy() method
    Console.WriteLine("Performing a memberwise clone of myName to myOldName");
    Name myOldName = Name.Copy(myName);
    Console.WriteLine("myOldName details:");
    myOldName.Display();
  }
   
}

           
          

   
 
using System;
class ObjectTest
{
   public int i = 10;
}

class MainClass2
{
   static void Main()
   {
      object a;
      a = 1;   // an example of boxing
      Console.WriteLine(a);
      Console.WriteLine(a.GetType());
      Console.WriteLine(a.ToString());

      a = new ObjectTest();
      ObjectTest classRef;
      classRef = (ObjectTest)a;
      Console.WriteLine(classRef.i);
   }
}

   
     

   
 
using System;
   
public class CPU {
  public string model;
   
  public CPU(string model) {
    this.model = model;
  }
   
  public void Start() {
    Console.WriteLine(model + " started");
  }
}
   
public class Intel : CPU {
  public bool convertible;
   
  public Intel(string model, bool convertible) : base(model) {
    this.convertible = convertible;
  }
}
   
public class AMD : CPU {
  public bool sidecar;
   
  public AMD(string model, bool sidecar) : base(model) {
    this.sidecar = sidecar;
  }
   
  public void PullWheelie() {
    Console.WriteLine(model + " pulling a wheelie!");
  }
   
}
   
   
class Test {
  public static void Main() {
    Intel myIntel = new Intel("MR2", true);
   
    // create a AMD object
    AMD myAMD = new AMD("V-Rod", true);
   
    // cast myAMD to CPU (upcast)
    CPU myCPU2 = (CPU) myAMD;
   
   
    // cast myCPU2 to AMD (downcast)
    AMD myAMD2 = (AMD) myCPU2;
   
    // myMotorCycle2 has access to all members of the AMD class
    Console.WriteLine("myAMD2.model = " + myAMD2.model);
    Console.WriteLine("myAMD2.sidecar = " + myAMD2.sidecar);
    myAMD2.Start();
    myAMD2.PullWheelie();

  }
}