need help with listbox items

[jac130]

I am trying to calculate the class average of student's grades. the student names are displayed in a list box, while their corresponding grade is displayed in a separate list box. calculate the average: # of students/ sum of their grades.(grades are numeric)

EX: John 90
sally 88
mike 75

I can't get it to add the sum of the grades i.e. (90+88+75). Also, I won't know how many students and grades the user will enter into the list. so it has to be able to add any number of grades.
any help would be great. thanks.

[QVeen72]

Hi,

You can Loop through and find the Average:

Dim i As Integer
Dim TMarks As Long
TMarks =0 
txtAvg.Text = "0.00"
For i = 0 To lstMarks.ListCount-1
    TMarks = TMarks + Val(lstMarks.List(i))
Next
If lstMarks.ListCount >0 Then
    txtAvg.Text = Format((TMarks/lstMarks.ListCount),"0.00")
End If
 

Regards
Veena

[jac130]

Thanks a lot, that helped. I also am having trouble with one other aspect. once the names and grades are displayed (in separate list boxes), there is a button, prompting the user to a certain grade, I must display a message box listing all of the student names below that certain grade. I've looped it to ask the user/ validate input, but it crashes before displaying the message box with all the names. Any thoughts? Here is a portion of my code:

Function GetBelowGrade() As Double
Dim onegrade As String = InputBox("please enter a positive number for the grade.")
Do While Not IsPositiveNumber(onegrade)
onegrade = InputBox("please enter a positive number for the grade.")
Loop
Dim i As Integer
For i = 0 To lstGrades.Items.Count - 1
Next

If lstGrades.Items(i) < onegrade Then
Return (MsgBox(lstStudents.Items(lstGrades.Items(i))))
End If
End Function

Private Sub btnBelowGrade_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnBelowGrade.Click
GetBelowGrade()

End Sub
End Class

any help would be great

[debasisdas]

why using inputbox twice ?

your variable is a string ,which you are using to compare using < perator without any conversion.

[jac130]

I changed it to this. but it says "onegrade" and "i" are used before they are assigned a value and could result in a null reference exception. Does that not matter?
i changed it to a string and it still crashes.
Function GetBelowGrade() As Double
Dim onegrade As String
Do While Not IsPositiveNumber(onegrade)
onegrade = InputBox("please enter a positive number for the grade.")
Loop
Dim i As String = lstGrades.Items(i)
If lstGrades.Items(i) < onegrade Then
Return MsgBox(lstGrades.Items(lstStudents.Items(i)))
End If

If lstGrades.Items(i) < onegrade Then
Return (MsgBox(lstStudents.Items(lstGrades.Items(i))))
End If
End Function

[jac130]

there would be two list boxes with names and grades: ex sally 90
mike 85

i click the getbelowgrade button, and am prompted to enter a grade, say 88. it should display Mike's name (he's below 88), but it crashes and highlights the Return line of the function, saying value 88 is not valid for index.
I'm stuck, here is my the portion of my code. Thanks.

Function GetBelowGrade() As String
Dim aGrade As String = InputBox("please enter a positive number for the grade.")
Do While Not IsPositiveNumber(aGrade)
aGrade = InputBox("please enter a positive number for the grade.")
Loop
Dim i As Integer
For i = 0 To lstGrades.Items.Count - 1 Step lstGrades.Items(i) < aGrade
Return MsgBox(lstStudents.Items(lstGrades.Items(i)))
Next
End Function


Private Sub btnBelowGrade_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnBelowGrade.Click
GetBelowGrade()

End Sub
End Class

[QVeen72]

Hi,

You may have One or more Students below the Average Grade, you need to Build a String and then Return List of the names..
Also, you are not returning anything, You can do with a Sub-Procedure
Check This Code:

Sub GetBelowGrade() As String
Dim aGrade As String = InputBox("please enter a positive number for the grade.")
Do While Not IsPositiveNumber(aGrade)
    aGrade = InputBox("please enter a positive number for the grade.")
Loop
Dim NGrade As Integer 
Dim strList As String =""
NGrade = Val(aGrade)
Dim i As Integer
'
For i = 0 To lstGrades.Items.Count - 1 
    If Val(lstGrades.Items(i)) < NGrade Then    
        strList = strList & lstStudents.Items(i) & ", "
    End If
Next
MsgBox strList
End Sub
 

Regards
Veena

[freefony]

Am so sorry am using this medium to get answers am working on a similar projects but unlike him am displaying my datas in a table and i need to calculate the value for just one of the column units to calculate the total units of all the courses registered by a student also my connection to the database cannot be accessed cos its said to be in a private dim even tho i decleared it in a public sub . am new to programming and i need all possible assistance

[jac130]

thanks. I did try that code and it helped greatly. Although, I did create it as a function, i was required to. i just returned a message box with the string list.
If i wanted to eliminate just the listbox of the grades (not the student names) from the interface, and store the grades into an array, then use the array in the functions,
I'm just lookin for adivce on how to start.for example.. in my current code i have:

dim grade as string=inputbox("please enter grades")
lstgrades.items.add(grades)

I have to delete the list box, how do i get those grades into an array? do i create a class level array: dim grades() as integer ? should i not specifiy a max index? or something like: dim grades() as integer = val(grade) ?
or create an array for each function. ?

any thoughts/adivce would be great