1- Write program that ask user to enter his age and then output yes if it is greater than or equal 20 and no otherwise.
   
               Sol:



			   {
				int age;
				Console.WriteLine("enter age");
				age=int.Parse(Console.ReadLine());
				if(age>=20)
				Console.WriteLine("yes");
                        else
                        Console.WriteLine("no");
	  }