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