Scripting Languages CS 5142, Fall 2013 hw02

Dates: Assigned Thursday 8/6/2013, due Friday 6/13/2013 at 6pm.
Topic: Objects, properties, call-backs (VBA)
Total points: 40
Instructions: Please put your solutions to VBA programming problems in a PowerPoint presentation. Put your answers to all remaining questions in a plain-text file, such as what you get when using Emacs, Vi, Notepad, or the “save as text only” feature in Word.

Reading Assignments

For lecture on 8/9/2013: Kirrily “Skud” Robert. perlintro(1) man page. Perl 5 documentation. Available on machines that have Perl properly installed, and also available online at http://perldoc.perl.org/perlintro.html

Concept Questions

hw02_1 Call-backs

1a.: (3 points) Give a short example for how in VBA forms, call-backs use mangled names.
1b.: (2 points) What is a disadvantage of the mangled-names approach to call-backs?
1c.: (3 points) Why are call-backs common in graphical user interfaces (GUIs)?
1d.: (2 points) Where else are call-backs common besides GUIs?

hw02_2 Properties

2a.

(3 points) Consider the VBA class Vector with the following code:

Public X As Double, Y As Double
Sub Class_Initialize()
  X = 0: Y = 0
End Sub
Public Property Get Length() As Double
  Length = Sqr(X ^ 2 + Y ^ 2)
End Property
Public Property Let Length(NewLen As Double)
  OldLen = Length
  If OldLen = 0 Then
    X = NewLen
    Y = 0
  Else
    X = X * NewLen / OldLen
    Y = Y * NewLen / OldLen
  End If
End Property

Give a short example for how writing the Length property affects the X and Y properties.

2b.

(4 points) If VBA would support only passive attributes, no active properties, how would you implement the Vector class?

2c.

(3 points) What is an advantage of the version with properties?

Programming exercises

hw02_3 Priority queue class

(10 points) Write a VBA class that implements a priority queue of Doubles. Your class should have two methods: Insert(key As Double) and ExtractMax() As Double. Your implementation should be robust with respect to queue size, growing the underlying data structures if necessary. Your code does not need to be efficient, so you do not need to find the fastest possible algorithm to solve this. Consider the following driver routine:

Sub Main_hw02_3()
  Dim Q As PriorityQueue
  Set Q = New PriorityQueue
  Q.Insert 3.1
  Q.Insert 4.2
  Q.Insert 0.5
  Q.Insert 1.9
  Debug.Print Q.ExtractMax
  Debug.Print Q.ExtractMax
  Debug.Print Q.ExtractMax
  Debug.Print Q.ExtractMax
End Sub

This should print 4.2, 3.1, 1.9, and 0.5, in other words, it should output the previously-inserted numbers in descending order by value.

hw02_4 Temperature conversion user form

(10 points) Implement a VBA user form that converts temperatures from Celsius to Fahrenheit and vice versa. Your form should look like this:

When the user enters a value in the “Celsius” field and presses the “To Fahrenheit” button, that should trigger a VBA call-back that shows the converted temperature in the “Fahrenheit” field, and vice versa. To solve this question, you will need to create a user form, and edit both the visual portion (with the controls) and the code sheet (with the call-backs). You can use the following driver to display the form:

Sub Main_hw02_3()
  Load frmTempConvert
  frmTempConvert.Show
  Unload frmTempConvert
End Sub

http://www.cs.cornell.edu/Courses/cs5142/2013fa/