' Basic Programming
' Ch. 8 Demo Program #3
' by Mr. Minich
' purpose - to illustrate an example of an event procedure calling a general
'              procedure

Option Explicit

Const MAX_CLASS_SIZE As Integer = 23   ' Only 23 students can be enrolled
                                       '   in the class since there are
                                       '   only 23 computers.

' ******* module-level variables ************

Dim mTestScores(1 To MAX_CLASS_SIZE) As Integer   ' student test scores
Dim mNumStudents As Integer                       ' total number of students

Private Sub cmdAddTestScore_Click()
    ' Purpose:       event procedure that prompts the user for a complete
    '                  set of student test scores
    ' Precondition:  None
    ' Postcondition: integer test scores will be placed into array of test scores
    ' Called By:     none
    ' Calls:         AddTestScore
    
    Call AddTestScore
    
End Sub

Private Sub cmdCalculateAverage_Click()
    ' Purpose:       event procedure that calculates class test average
    ' Precondition:  at least one score is entered into array, mTestScores,
    '                   otherwise, division-by-zero error will occur
    ' Postcondition: class test average will be displayed in a label
    
    Dim Subtotal As Integer     ' subtotal of all student test scores
    Dim ClassAverage As Single  ' class test average
    Dim J As Integer            ' loop variable
    
    For J = 1 To mNumStudents
        Subtotal = Subtotal + mTestScores(J)
    Next J
    
    ClassAverage = Subtotal / mNumStudents  ' computing class average
    lblClassAverage.Caption = ClassAverage  ' displaying class average
      
End Sub


Private Sub cmdDisplayScores_Click()
    ' Purpose:       event procedure that displays the student test scores in a listbox
    ' Precondition:  scores are entered into an array
    ' Postcondition: test scores will be placed into a listbox
    
    Dim J As Integer            ' loop variable
    
    For J = 1 To mNumStudents
        lstDisplayedScores.AddItem mTestScores(J)
    Next J
    
End Sub

Private Sub AddTestScore()
    ' Purpose:          event procedure that prompts the user for a complete
    '                     set of student test scores
    ' Precondition:     none
    ' Postcondition:    integer test scores will be placed into array of test scores
    ' Called By:        AddTestScore_Click
    ' Calls:            None
    
    Dim J As Integer           ' loop variable
    Dim ExitFlag As Integer    ' flag variable to control user input
    Dim StudentNum As Integer  ' keeps track of current student number

    Dim UserPrompt As String   ' prompt for next student test score personalized
                               '    with the current student number
                               
    ' ***** Initializing local variables *****
    
    ExitFlag = 0               ' set flag to zero so that the loop iterates
    StudentNum = 1
                               
    MsgBox ("Warning: Inputting new scores will overwrite previous scores!" & vbCr & _
             "Enter a score of -1 to indicate that all scores have been entered.")
    
                                ' -1 is a sentinel value to indicate the end of the user's input
    
    ' ***** Obtaining user input *************
    
    Do
       UserPrompt = "Enter the test score for student number " & StudentNum & ": "
       mTestScores(StudentNum) = InputBox(UserPrompt)       ' obtaining the next test score
       
       If mTestScores(StudentNum) = -1 Then
          mNumStudents = StudentNum - 1            ' set the total number of students
                                                   '    subtracting one so that an extra
                                                   '    student is not counted
          ExitFlag = 1
       Else
          StudentNum = StudentNum + 1              ' increment to next student number
       End If
    
    Loop While (ExitFlag <> 1 And mNumStudents < MAX_CLASS_SIZE)
    
    
End Sub