Public Class Form1
    Inherits System.Windows.Forms.Form

#Region " Windows Form Designer generated code "

    Public Sub New()
        MyBase.New()

        'This call is required by the Windows Form Designer.
        InitializeComponent()

        'Add any initialization after the InitializeComponent() call

    End Sub

    'Form overrides dispose to clean up the component list.
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If Not (components Is Nothing) Then
                components.Dispose()
            End If
        End If
        MyBase.Dispose(disposing)
    End Sub

    'Required by the Windows Form Designer
    Private components As System.ComponentModel.IContainer

    'NOTE: The following procedure is required by the Windows Form Designer
    'It can be modified using the Windows Form Designer.  
    'Do not modify it using the code editor.
    Friend WithEvents TxtScore As System.Windows.Forms.TextBox
    Friend WithEvents TxtGrade As System.Windows.Forms.TextBox
    Friend WithEvents BtnGrade As System.Windows.Forms.Button
    Friend WithEvents BtnGradeElseIf As System.Windows.Forms.Button
    Friend WithEvents BtnCase As System.Windows.Forms.Button
    Friend WithEvents BtnIS As System.Windows.Forms.Button
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
        Me.TxtScore = New System.Windows.Forms.TextBox
        Me.TxtGrade = New System.Windows.Forms.TextBox
        Me.BtnGrade = New System.Windows.Forms.Button
        Me.BtnGradeElseIf = New System.Windows.Forms.Button
        Me.BtnCase = New System.Windows.Forms.Button
        Me.BtnIS = New System.Windows.Forms.Button
        Me.SuspendLayout()
        '
        'TxtScore
        '
        Me.TxtScore.Location = New System.Drawing.Point(168, 40)
        Me.TxtScore.Name = "TxtScore"
        Me.TxtScore.Size = New System.Drawing.Size(88, 20)
        Me.TxtScore.TabIndex = 0
        Me.TxtScore.Text = ""
        '
        'TxtGrade
        '
        Me.TxtGrade.Location = New System.Drawing.Point(168, 88)
        Me.TxtGrade.Name = "TxtGrade"
        Me.TxtGrade.ReadOnly = True
        Me.TxtGrade.Size = New System.Drawing.Size(88, 20)
        Me.TxtGrade.TabIndex = 1
        Me.TxtGrade.Text = ""
        '
        'BtnGrade
        '
        Me.BtnGrade.Location = New System.Drawing.Point(160, 128)
        Me.BtnGrade.Name = "BtnGrade"
        Me.BtnGrade.Size = New System.Drawing.Size(72, 32)
        Me.BtnGrade.TabIndex = 2
        Me.BtnGrade.Text = "Grade"
        '
        'BtnGradeElseIf
        '
        Me.BtnGradeElseIf.Location = New System.Drawing.Point(160, 192)
        Me.BtnGradeElseIf.Name = "BtnGradeElseIf"
        Me.BtnGradeElseIf.Size = New System.Drawing.Size(80, 32)
        Me.BtnGradeElseIf.TabIndex = 3
        Me.BtnGradeElseIf.Text = "Grade"
        '
        'BtnCase
        '
        Me.BtnCase.Location = New System.Drawing.Point(160, 240)
        Me.BtnCase.Name = "BtnCase"
        Me.BtnCase.Size = New System.Drawing.Size(88, 32)
        Me.BtnCase.TabIndex = 4
        Me.BtnCase.Text = "Grade(Case)"
        '
        'BtnIS
        '
        Me.BtnIS.Location = New System.Drawing.Point(32, 168)
        Me.BtnIS.Name = "BtnIS"
        Me.BtnIS.Size = New System.Drawing.Size(112, 32)
        Me.BtnIS.TabIndex = 5
        Me.BtnIS.Text = "Grade (Is)"
        '
        'Form1
        '
        Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
        Me.ClientSize = New System.Drawing.Size(292, 273)
        Me.Controls.Add(Me.BtnIS)
        Me.Controls.Add(Me.BtnCase)
        Me.Controls.Add(Me.BtnGradeElseIf)
        Me.Controls.Add(Me.BtnGrade)
        Me.Controls.Add(Me.TxtGrade)
        Me.Controls.Add(Me.TxtScore)
        Me.Name = "Form1"
        Me.Text = "Form1"
        Me.ResumeLayout(False)

    End Sub

#End Region

    Private Sub BtnGrade_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnGrade.Click
        Dim score As Double
        score = Convert.ToDouble(TxtScore.Text)
        Dim grade As String
        If score >= 90 Then
            grade = "A"
        Else
            If score >= 80 Then
                grade = "B"
            Else
                If score >= 70 Then
                    grade = "C"
                Else
                    If score >= 60 Then
                        grade = "D"
                    Else
                        grade = "F"
                    End If
                End If
            End If
        End If
        TxtGrade.Text = grade
    End Sub

    Private Sub BtnGradeElseIf_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnGradeElseIf.Click
        Dim score As Double
        score = Convert.ToDouble(TxtScore.Text)
        Dim grade As String
        If score >= 90 Then
            grade = "A"
        ElseIf score >= 80 Then
            grade = "B"
        ElseIf score >= 70 Then
            grade = "C"
        ElseIf score >= 60 Then
            grade = "D"
        Else
            grade = "F"

        End If
        TxtGrade.Text = grade

    End Sub

    Private Sub BtnCase_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnCase.Click
        Dim score As Double
        score = Convert.ToDouble(TxtScore.Text)
        Dim grade As String
        Select Case score
            Case 90 To 100
                grade = "A"
            Case 80 To 89.999999
                grade = "B"
            Case 70 To 79.999999
                grade = "C"
            Case 60 To 69.999999
                grade = "D"
            Case Else
                grade = "F"
        End Select
        TxtGrade.Text = grade
    End Sub

    Private Sub BtnIS_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnIS.Click
        Dim score As Double
        score = Convert.ToDouble(TxtScore.Text)
        Dim grade As String
        Select Case score
            Case Is >= 90
                grade = "A"
            Case Is >= 80 ' would do the rest down below like this too
                grade = "B"
            Case 70 To 79.999999
                grade = "C"
            Case 60 To 69.999999
                grade = "D"
            Case Else
                grade = "F"
        End Select
        TxtGrade.Text = grade
    End Sub
End Class