lecture notes

Nesting: putting one loop in another
Loop thru values of X in (0 thru 2)
    Loop thru values of y in (0 thru 3)
        Print (x, y)
    End Loop
End Loop

LISTS.TXT
    ' the names of other phonebook files
    CLIENTS.TXT
    FRIENDS.TXT
    KINFOLK.TXT


Loop thru filenames in the LISTS.TXT file
    Open the current filename
    Loop thru the entries in the current file
        see if name occurs in current file
    End Loop
End Loop

Private Sub btnDisplay_Click(...) Handles btnDisplay.Click
  Dim foundFlag As Boolean
  Dim fileName As String
  Dim name As String = ""
  Dim phoneNum As String = ""
  Dim sr1 As IO.StreamReader = IO.File.OpenText ("LISTS.TXT")

  txtNumber.Text = "Name not found."
  ' by the way, i use a goto to break out multiple
  ' levels when we find the actual word
  Do While sr1.Peek <> -1
    fileName = sr1.ReadLine
    Dim sr2 As IO.StreamReader = IO.File.OpenText(fileName)
    Do While sr2.Peek <> -1
      name = sr2.ReadLine
      phoneNum = sr2.ReadLine
      If name = txtName.Text Then
    txtNumber.Text = name & "     " & phoneNum
        Goto Here
      Endif
    Loop
  Loop
  sr1.Close()
Here:

End Sub

HW:
Processing Lists of Data with Do Loops
question 20-24, even

Write a program to find and display the largest of a collection of positive numbers contained in a text file. (Test the program with the collection of numbers 89, 77, 95, and 86.)

Dim max as Integer
max = 0

Do While sr.Peek <> -1
    current = sr.ReadLine
    ' is my optimistic assumption wrong?
    If current > max Then
        max = current
    EndIf
Loop

Debug.Print("The max value is: " & max)

lecture

Write a function that returns n factorial

txtBox1.Text = fact(5)

1) where do i start?
2) where do i end?
3) how do i get to the next step?

Function fact(byval n as integer) As integer
    dim i as integer
    dim prod as integer
    i = 1
    prod = 1

    Do
        prod = prod * i
        i += 1
    Loop Until i = n + 1
    Return prod
End Function

prod is a accumulator
off by one error
we calculated factorial using "iteration"
"iteration" is a fancy name for loops

write me a function which is the SUM of the nums from 1 to n:

Function sum(byval n as integer) As integer
    dim i as integer
    dim total as integer
    i = 1
    total = 0

    Do
        total = total + i
        i += 1
    Loop Until i > n
    Return total
End Function

sr.Peek will return -1 if reached EOF (end of file)

lets say i want to read firstname, lastname, and print it out.

1) where do i start?
2) where do i end?
3) how do i get to the next step?

Dim sr As IO.StreamReader
sr = IO.File.OpenText("c:\josh\Names.txt")
Dim firstname, lastname as String

Do While sr.Peek <> -1
    firstname = sr.ReadLine
    lastname = sr.ReadLine
    ListBox1.Items.Add("first: " & firstname,  & vbTab & "last" & lastname)
Loop


Private Sub btnDisplay_Click(...) Handles btnDisplay.Click
  Dim name, phoneNum As String
  Dim sr As IO.StreamReader = IO.File.OpenText("PHONE.TXT")
  ' pessimistic assumption
  txtNumber.Text = "Name not found."

  Do While sr.Peek <> -1
    name = sr.ReadLine
    phoneNum = sr.ReadLine
    If name = txtName.Text Then
       ' my pessimistic assumption was proven false
       txtNumber.Text = name & "    " & phoneNum
    ' make things faster; this is optional
    Exit Do
    EndIf
  Loop

  sr.Close()
End Sub

lecture notes

q 23

c = -40

f = (9/5)*c + 32
ListBox1.Items.Add("c:" & c & vbTab & "f:" & f)


the actual code:
Public Class Form1

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        c = -40
        Do
            f = (9 / 5) * c + 32
            ListBox1.Items.Add("c:" & c & vbTab & "f:" & f)
            c += 5
        Loop Until c > 40
    End Sub
End Class

q 25:

1) where do we start (initialization)?
2) where do we end? (terminating condition)
3) how do we get there? each step (increment)

'Dim pop as Double
'pop = 6.5

Dim pop as Long
pop = 6.5 * 10 ^ 9
Const percent = 1.2 / 100
Dim year as Integer = 2006

Do
 ListBox1.Items.Add("year:" & year & vbTab & "pop:" & pop)
 year += 1
 pop = pop + pop * percent
Loop Until pop >= 10 * 10^9

ListBox1.Items.Add("year:" & year & vbTab & "pop:" & pop)

Different roles for variables when it comes to loops
1) loop control variable
2) counter
3) accumulator
4) flag

q 27:
Write a program to display all the numbers between 1 and 100 that are part of the Fibonacci sequence. The Fibonacci sequence begins 1, 1, 2, 3, 5, 8,..., where each new number in the sequence is found by adding the previous two numbers in the sequence.

prev = 1
cur = 1

Do
 ListBox1.Items.Add("num:" & vbTab & cur)
 temp = prev
 prev = cur
 cur = temp + cur
Loop Until cur > 100


' now, using mathematic notation
Fn = 1
Fn_1 = 0

Do
 ListBox1.Items.Add("num:" & vbTab & Fn)
 Fn_2 = Fn_1
 Fn_1 = Fn
 Fn = Fn_1 + Fn_2
Loop Until Fn > 100

using iteration to calculate Fibonacci

HW: Do Loops, q 24-36, evens

lecture

Goto statement
Goto label

jmp instruction in assembler
cmp, followed by a jnz instruction

for loop, while loop, examples of syntactic sugar


in BASIC, my first program:
10 Print "Hello"
20 Goto 10

in Visual Basic:
here:
    Debug.Print("Hello")
    Goto here
    Debug.Print("Goodbye")

an infinite loop never ends
how would we do this without Gotos?

Do
    Debug.Print("Hello")
Loop

    I = 0
here:
    Debug.Print("Hello" & I)
    I = I + 1
    If i < 3 Then
        Goto here
    EndIf

I = 0
Do
    Debug.Print("Hello" & I)
    I = I + 1
Loop While i < 3

' this is called a post-test

what if we want a pretest?
I = 0
Do While i < 3
    Debug.Print("Hello" & I)
    I = I + 1
Loop

I = 0
goto there
here:
    Debug.Print("Hello" & I)
    I = I + 1
there:
    If i < 3 Then
        Goto here
    EndIf

So why don't we use Gotos?!
1) simpler
2) higher
3) more controlled
4) spaghetti code

http://en.wikipedia.org/wiki/Spaghetti_code

10 i = 0
20 i = i + 1
30 PRINT i; " squared = "; i * i
40 IF i >= 10 THEN GOTO 60
50 GOTO 20
60 PRINT "Program Completed."
70 END

FOR i = 1 TO 10
    PRINT i; " squared = "; i * i
NEXT i
PRINT "Program Completed."
END

a move to eliminate gotos
Goto statement considered harmful

http://www.u.arizona.edu/~rubinson/copyright_violations/Go_To_Considered_Harmful.html

Goto statement considered harmful considered harmful

rules for using goto:
1) it should always be fairly close
2) only goto above you, never below you



  Dim response As Integer, quotation As String = ""

  Do
    response = CInt(InputBox("Enter a number from 1 to 3."))
  Loop Until response >= 1 And response <= 3

functions - return a value, which we can use


x = Int(2.6)
y = Int(7.6) + 6

Public Class Form1
    Function Foo() As String
        Dim x As Integer
        x = 7
        Return "Hello"
    End Function

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim s As String
        s = Foo()
        Button1.Text = s
    End Sub
End Class


y = f(x)

money today is worth more than money a year from now
FV = PV * (1+RATE)^NPER


but can compount mult times per year. need divide by freq

HW: Chapter 4 Programming Projects
 1-4

notes from lecture

static, local, class-level variables
lifetime vs. scope
final is wendesday, 12/15, from 4-6 PM in our regular room

Midterm answers

Midterm for class 1
Midterm for class 2