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CS109 Final Name ________________________
100 Points Total
This exam is open book and you are welcome to use a computer in the lab. If you are
unable to come up with a full answer, write down pseudocode or your thought processes
for partial credit. You have 2 hours. Good Luck!
1. (24 pts) Short Answer. Provide brief (1-3 sentence) answers to the following:
a) Describe what difference there is, if any, between the following two subroutines
(aside from the words ByVal and ByRef):
Public Sub ChangeArray1(ByVal ary() As Integer) ary(0) = 5 End Sub
Public Sub ChangeArray2(ByRef ary() As Integer) ary(0) = 5 End Sub
b) How many array entries are created by the following statement?
Dim a(10) As Integer
c) Describe what a breakpoint is and how the debugging tool in Visual Studio can be
used to track down bugs.
d) What control would you use if you wanted to execute some code every 5 seconds?
e) How can the OOP (Object Oriented Programming) principle of inheritance help
us eliminate redundant code?
f) What role does SQL play in the creation of a database application?
2. (16 pts) Find the Bugs
All of the following code snippets have one or more bugs. Identify each one and fix the
bug(s). Assume the necessary code is in place to make a working program (e.g. the form
exists, the code is within some event, etc.).
a) The following should continue until the user enters a number from 1-3:
Dim i As Integer = - While ((i <> 1) Or (i <> 2) Or (i <> 3)) i = CInt(InputBox("Enter either 1, 2, or 3")) End While
b) The following code should print “Big” or “Bigger”
Dim i As Integer i = CInt(InputBox("Enter a integer.")) If (0 < i < 10) Then Console.WriteLine("Big") ElseIf (10 <= i) Then Console.WriteLine("Bigger") End If
(problem continues on the next page)
3. (15 points) Loopy with Arrays
The function below takes as input an array of strings. The array contains a list of names.
Complete the function such that it returns True if one or more of the entries in the array
is the name "Bobo". If "Bobo" is not any of the names in the array then the function
should return False.
You can use aryNames.Length to get the length of the array.
Assume that data is stored beginning at aryNames(0).
Function ContainsBobo(ByVal aryNames() As String) As Boolean
End Function
4. (15 pts) Nested Loops
Rewrite the following code such that the functionality remains the same, but uses two
while loops instead of the for loops.
Dim i, j As Integer
For i = 10 To 0 Step - For j = 1 To i Console.Write("*") Next Console.WriteLine() Next
5) (10 points) Classes and Constructors
Given the following class:
Public Class MyClass Public val As Integer = 1
Public Sub New() val = 2 End Sub
Public Sub New(ByVal newNum As Integer) val = newNum End Sub
Public Sub Print() Console.WriteLine(val) End Sub End Class
What would this code output to the Console?
Dim r1 As New MyClass Dim r2 As New MyClass(3)
r1.Print() r2.Print()
b) Consider the class below:
Public Class SimpleClass Public val As Integer End Class
We said that it is generally better to make the class variables Private, with a Public
property as follows:
Public Class BetterSimpleClass Private val As Integer
Public Property Value() As Integer Get Return val End Get Set(ByVal Value As Integer) val = Value End Set End Property
End Class
Why is the organization of BetterSimpleClass usually considered a better
technique than that of SimpleClass?
7. (10 points) Food Sales
Now that VB.NET is over and summer is here, it means selling food from your booth at
the State Fair. You have an array of foods that you sell, e.g.:
Dim aryFoods() As String = {"Elephant Ears", _ "Turkey Leg", "Salmon Taco", "Deep Fried Twinkie"}
Each food is given an ID, which is its index in the array. For example, 0 refers to
Elephant Ears, 1 refers to Turkey Leg, 2 refers to Salmon Taco, and 3 refers to Deep
Fried Twinkies.
At the end of the day you get a log of food sales with the ID of each food in the order it is
sold. The log is stored in an array. For example, if you sold, in order: two elephant ears,
two turkey legs, one elephant ear, one twinkie, one salmon taco, and one twinkie, then
the array would look like this:
Dim arySaleLog() As Integer = {0, 0, 1, 1, 0, 3, 2, 3}
Write a subroutine called CountSales that inputs both arrays as parameters and
outputs to the Console window the number of sales for each food.
Given the arrays defined above,
CountSales(aryFoods, arySaleLog)
Would output:
You sold 3 Elephant Ears You sold 2 Turkey Leg You sold 1 Salmon Taco You sold 2 Deep Fried Twinkie
Make sure that your subroutine works for any array of foods, not just the example given
here. For example, it should also work if there were 10 foods in the array, with ID’s from
0 to 9. Hint: Create a separate array to count the number of each food item. Use
aryFoods.Length to get the number of items in the array.
