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I need someone to explain to me exactly how this code works. Please help

Posted on 2008-11-02
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Last Modified: 2013-11-26
I got this code from an expert. The program permutates all the letters of a phone number input. The program works great but i need help understanding it so if someone could help that would be great!
Public Class Lab4

    Public Function makeCharList(ByVal chars As String) As List(Of Char)

        Dim charsList As New List(Of Char)()
 

        For Each c As Char In chars.Trim().ToCharArray()

            charsList.Add(c)

        Next
 

        Return charsList

    End Function
 

    Private Sub generate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles generate.Click

        'Use of a dictionary may be better, it uses same concept as KeyValuePair but already has it in a collection

        'Therefore, you will not have to recreate the wheel

        Dim dict As New Dictionary(Of Char, List(Of Char))()

        Dim words As New List(Of String)() 'To store word possibilities

        Dim wordsTemp As New List(Of String)() 'Temp word lists as needed

        Dim listTemp As New List(Of Char)() 'Temp character list
 

        'Adds and assigns each digit to an array of characters

        dict.Add("0", makeCharList(""))

        dict.Add("1", makeCharList(""))

        dict.Add("2", makeCharList("ABC"))

        dict.Add("3", makeCharList("DEF"))

        dict.Add("4", makeCharList("GHI"))

        dict.Add("5", makeCharList("JKL"))

        dict.Add("6", makeCharList("MNO"))

        dict.Add("7", makeCharList("PQRS"))

        dict.Add("8", makeCharList("TUV"))

        dict.Add("9", makeCharList("WXYZ"))
 

        Dim phoneNo As String = phonenumber.Text.Trim() 'assigns value of textbox control to local variable
 

        'Goes through each digit of your phone number
 

        For Each digit As Char In phoneNo.ToCharArray()
 

            listTemp = dict(digit)

            If listTemp.Count > 0 Then

                '''''''''' setup words list ''''''''''
 

                wordsTemp.Clear()

                If words.Count < 1 Then

                    wordsTemp.Add("")

                Else

                    wordsTemp.AddRange(words)

                    words.Clear()

                End If
 
 

                For Each word As String In wordsTemp

                    For Each c As Char In listTemp

                        words.Add(word & c)
 

                    Next

                Next

            End If

        Next
 

        MsgBox(String.Format("Writing {0} words to list", words.Count))

        lbWords.Items.Clear()

        lbWords.Items.AddRange(words.ToArray())

        MsgBox("Generate process complete!")
 
 

    End Sub
 

End Class

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Question by:ajh305
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Mysidia earned 500 total points
ID: 22862739
It seems self-explanatory.  

The code declares and sets up  'dict'  a hash indexed by the digits 0 through 9,
with a stored value of the letters  associated with that digit
i.e.  "2" to "ABC"
...

Next a variable 'phoneNo'  is assigned to the current value of a textbox at the start of the procedure.

A temporary list "words" starts in the empty state.

A for loop examines each character.
  Within one iteration of the for loop
   the digit is examined

   'listTemp'  is assigned to the list of characters from "dict"
    i.e.  if    the current digit is "2"  then  listTemp  is the list with 3 items,
    A, B, C,
    if current digit is "3"  then  listTemp  is D, E, F,  and so on.

    A temporary list  "wordsTemp"   is reset so it contains no items.

    If there are any items in the "words"  temporary list, they are added to wordsTemp
    and  "words" is again reset to an empty state.

    For every word in the  "wordsTemp"  list
       For every item in the "listTemp"  list of characters
          the word in wordsTemp   PLUS the character in listTemp
          is added to the "words"  list
         

    The iteration of  the outer 'for' loop completes and the next digit is now being examined.

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