this can be a solution

vb Code:
  1. private str as string = "abc" 'at least two characters in the string

  2. private counter as integer = 0

  3.  
  4. private sub form_load(Sender as object, e as eventArgs) handles Form1.Load

  5.   Sound(str.Chars(counter))

  6.   counter += 1

  7. end sub

  8.  
  9. private textBox1.keyPress(Sender as object, e as ByVal e As System.Windows.Forms.KeyPressEventArgs) handles TextBox1.KeyPress

  10.       sound(str.Cahrs(counter))

  11.       counter += 1 

  12.  
  13.   if counter = str.length then

  14.     messageBox.Show("Something")

  15.   ens if

  16. end sub