Question about program flow

[trippeer]

I am working my way through this book and I am a bit confused about the flow of this sample program:

' Fig. 3.4: Interest.vb
' Calculating compound interest.

Imports System.Windows.Forms

Module modInterest

   Sub Main()
      Dim amount, principal As Decimal ' dollar amounts
      Dim rate As Double               ' interest rate
      Dim year As Integer              ' year counter
      Dim output As String             ' amount after each year

      principal = 1000
      rate = 0.05

      output = "Year" & vbTab & "Amount on deposit" & vbCrLf

      ' calculate amount after each year
      For year = 1 To 10
         amount = principal * (1 + rate) ^ year
         output &= year & vbTab & _
            String.Format("{0:C}", amount) & vbCrLf
      Next

      ' display output
      MessageBox.Show(output, "Compound Interest", _
         MessageBoxButtons.OK, MessageBoxIcon.Information)
   End Sub  ' Main

End Module  ' modInterest

The code displays a message box with 10 years' interest, but I don't see why. Since the message box code appears after the loop is complete, it seems to me that it would only display the last value of output, not all 10. I am really new to visual programming, and I can't figure out why the display code is not inside the loop. My background is in C/C++ so I am having trouble figuring this out. Thanks for any help.

[<ABX]

Imports System.Windows.Forms
 
Module modInterest
 
   Sub Main()
      Dim amount, principal As Decimal ' dollar amounts
      Dim rate As Double               ' interest rate
      Dim year As Integer              ' year counter
      Dim output As String             ' amount after each year
 
      principal = 1000
      rate = 0.05
 
      output = "Year" & vbTab & "Amount on deposit" & vbCrLf
 
      ' calculate amount after each year
      For year = 1 To 10
         amount = principal * (1 + rate) ^ year
         'this is because the values are being appended to this string here
         'notice the &= operator instead of just plain =
         'this adds the string on to it, instead of setting it to the value
         'if you were to change this to = then it would give you your expected
         'result.
         output &= year & vbTab & _
            String.Format("{0:C}", amount) & vbCrLf
      Next
 
      ' display output
      MessageBox.Show(output, "Compound Interest", _
         MessageBoxButtons.OK, MessageBoxIcon.Information)
   End Sub  ' Main
 
End Module  ' modInterest

If your a C/C++ developer you may be more at home with C# than VB.Net.

[trippeer]

If your a C/C++ developer you may be more at home with C# than VB.Net.

But I want to learn VB.

This is not a "help me pick a programming language" post. I had a question about VB program flow.

[<ABX]

I just added that as I thought it might help you, did you not notice the Extra comments I added to your code?

[trippeer]

I just added that as I thought it might help you, did you not notice the Extra comments I added to your code?

Ah, now I see, thank you. It is printing the final value of output, it is just that output contains several vbCrLfs. Thank you, and sorry I didn't notice your comments.