/*
                  CSC 123 C# Warm up assignment

		  Due one week from date assigned

Part I:

1. C# is basically like Java, but there are some unique features.  One of these
is the "delegate" construct, which allows you to write higher-order functions.
That is, functions that take other functions as arguments (such as map, fold,
howmany, etc ...).  Study the three sample programs on the homepage that
uses delegates to understand how it works.  Then write the delegate 

public delegate bool boolFun(int x);

( alternatively, with C# 2010, you can use Func<int,bool> )

And implement your favorite scheme/perl function "howmany" on arrays.
That is, it should return the number of elements in an arrays of
integers (see delegates.cs) for which the delegate function returns
true. Demonstrate your program with at least two instantiations of the
the delegate template.


2. The .Net API contains a built-in class called ArrayList, which works like
the array/list structures in Perl.  Go to the MSDN website and search for
"ArrayList" for the complete docs, but the following example should be more
than enough.  The structure can be used like a list or an array.  As the
example indicates, you can store data of different types in the same ArrayList.
That's because both strings and integers are implicitly type-cast to 
the ultimate supertype "object".  As far as the compiler is concerned, each
element of the ArrayList is an object.  You cannot say A[3]+2 even if you know
that A[3] is an integer - because all the compiler knows is that it's
an object.  Before you can use the element as an integer, you must explicitly
type-cast it back to an int.  Study the small program to make sure you 
understand this point.  Remove the type-cast (int) operator in the program
and observe what happens.  Does it even compile?

What if you try to use A[1] ("world") as an integer?  That is, what if
you try to add 2 to A[1] by first casting it to an integer?  What kind of
error do you get (compile time or runtime?) Record the behavior and EXPLAIN
WHY. 

**You need to adopt the "howmany" higher-order function to work with ArrayLists
instead of simple arrays.  Remember to type-cast before you use the elements
as integers.

<OPTION> Convert Arraylist to Generic Lists (see the second delegates example)

*/

using System;
using System.Collections;   // needed to use ArrayList

public class cshw1
{
  public static void Main()
  {
     ArrayList A = new ArrayList(); // creates empty array list
     A.Add("hello"); // add works like "push" - adds to end of list
     A.Add("world");
     A.Add(30);
     A.Add("blah"); 
     Console.WriteLine("there are "+A.Count+" objects in the ArrayList"); 

     A[3] = (int)A[2] + 1;  // what will happen if there's no (int) ?

     A.Remove("blah"); // removes the specified element
     foreach (object x in A) { Console.WriteLine(x); } 
  } // Main
}
// Compile this program with  csc cshw1.cs  and run it with  .\cshw1.exe


/*
Part II:

Start with the following class
*/

class A 
{
  public virtual void g() {Console.WriteLine("this is A.g()");}
}

/* Now write a subclass B so that the following code will have the
   indicated behavior. hint: you'll need to override g and introduce a
   new variable z.

   class B : A
   { ...
*/

public class part2 // put in file called part2.cs
{
 public static void Main()
 {
    A n = new B();
    n.g();  // should print something other than "this is A.g()"

    //Console.WriteLine( B.z );  // should be compiler error if uncommented
    Console.WriteLine( ((B)n).z );  // should print some number
    
    A m = new A();
    Console.WriteLine( ((B)m).z ); // what does this do?  Explain what's
                                   // happening here.
 }
}