Stepped table lookup in VB? - vb.net

Question

I use this code from the book that illustartes exampel of stepped table looup:
Imports System
Imports Microsoft.VisuaLBasic
Public Module Module1
Public Sub Main()
Dim rangeLimit() as Double = {50.0, 65.0, 75.0, 90.0, 100.0}
Dim grade() as String = {"F", "D", "C", "B", "A"}
Dim maxGradeLevel = grade.length - 1
Dim gradeLevel = 0
Dim studentGrade = "A"
Dim studentScore = 50
While((studentGrade = "A") and (gradeLevel < maxGradeLevel))
if(studentScore < rangeLimit(gradeLevel)) then
studentGrade = grade(gradeLevel)
End if
gradeLevel = gradeLevel + 100
End While
Print(studentGrade)
End Sub
End Module
Code is here
I wonder how does it work and how to fix this error after compiling:
Run-time exception (line -1): Conversion from string "A" to type 'Integer' is not valid.

Answer 1

You probably want Console.WriteLine() instead of Print().
Also:
Imports System
Imports System.Linq
Public Module Module1
Public Sub Main()
Dim studentScore As Double = 50.0
Console.WriteLine(GetGrade(studentScore))
End Sub
Public Function GetGrade(score As Double) As String
Dim gradeTable = {
(50.0, "F"),
(65.0, "D"),
(75.0, "C"),
(90.0, "B"),
(100.0, "A")
}
Return gradeTable.First(Function(g) g.Item1 >= Score).Item2
End Function
End Module
See it work here:
https://dotnetfiddle.net/CKTNCE
Personally, though, I prefer to use the minimum grade instead of the maximum for the boundaries. I find it far more likely you'll have extra credit push a score above 100 than you'll have something send you a negative score, and using maximum grades causes problems in that situation:
Imports System
Imports System.Linq
Public Module Module1
Public Sub Main()
Dim studentScore As Double = 50.0
Console.WriteLine(GetGrade(studentScore))
End Sub
Public Function GetGrade(score As Double) As String
Dim gradeTable = {
(90.0, "A"),
(75.0, "B"),
(65.0, "C"),
(50.0, "D"),
( 0.0, "F")
}
Return gradeTable.First(Function(g) g.Item1 >= Score).Item2
End Function
End Module
You also need to be careful with your equality comparisons. >= and > mean different things, and only one is correct.