entering value for scale using textboxes

Hello..i have a programm that can plot a sin and tan graph.now i want the user to be able to enter the scale value,in my case is Xa,Xe,Ya,Ye by typing in the value in the textboxes.i have created 4 textboxes,1 comboBox and 1 button.but now it wont run anymore.can some one help me??thanx..i have two forms.Form2 is used to plot the graph(sin or tan) and Form1 is used for the user to enter the value in the textboxes.

------------------------------------------------------------------------

FORM2:

VB Code:

Imports System.Drawing.Printing
Imports System.IO
Public Class Form2
    Inherits System.Windows.Forms.Form
    Dim int_X0, int_Y0, int_i As Integer
    Dim single_Xa, single_Xe, single_Ya, single_Ye As Integer
    Dim x_Array(), y_Array(), Xa, Xe, Ya, Ye As Single
    Dim int_color As System.Drawing.Pen
    
  Private Sub Drawing_load(ByVal sender As Object,ByValAsSystem.EventArgs) Handles Me.Load
 
        XA = Val(Form1.TextBox1.Text)
        Xe = Val(Form1.TextBox2.Text)
        Ya = Val(Form1.TextBox3.Text)
        Ye = Val(Form1.TextBox4.Text)
 
        If Form1.ComboBox1.Text = "Sinus" Then
            main()
        ElseIf Form1.ComboBox1.Text = "Tan" Then
            main1()
 
        End If
        'PictureBox1.Image = bmp
    End Sub
    
   Sub main()
        ReDim x_Array(628), y_Array(628)
        For int_i = 0 To UBound(x_Array) Step 1
            x_Array(int_i) = int_i / 100 - 5
        Next
        Sinus(x_Array)
        'Tan(x_Array)
        Plot(x_Array, y_Array, Pens.Gold, Xa, Xe, Ya, Ye)
    End Sub
    
    Sub main1()
        ReDim x_Array(628), y_Array(628)
 
        For int_i = 0 To UBound(x_Array) Step 1
            x_Array(int_i) = int_i / 100 - 5
        Next
        Tan(x_Array)
        Plot(x_Array, y_Array, Pens.Gold, Xa, Xe, Ya, Ye)
    End Sub
  
Function Tan(ByVal x_Array)
        For int_i = 0 To UBound(x_Array) Step 1
            y_Array(int_i) = Math.Tan(x_Array(int_i))
        Next
        Return y_Array
    End Function
 
Function Sinus(ByVal x_Array)
        For int_i = 0 To UBound(x_Array) Step 1
            y_Array(int_i) = Math.Sin(x_Array(int_i))
        Next
        Return y_Array
    End Function
 
Function Plot(ByVal x_Array, ByVal y_Array, ByVal int_color, ByVal single_Xa, ByVal single_Xe, ByVal single_Ya, ByVal single_Ye)
        Dim bmp As New Bitmap(PictureBox1.Width, PictureBox1.Height)
        Dim g As System.Drawing.Graphics = Graphics.FromImage(bmp)
        int_X0 = 50
        int_Y0 = 600
        g.TranslateTransform(int_X0, int_Y0)
        Dim P1 As New System.Drawing.Point(0, 0)
        Dim P2 As New System.Drawing.Point(600, 0)
        Dim P3 As New System.Drawing.Point(0, -600)
        g.DrawLine(New Pen(Color.Black, 2), P1, P2)
        g.DrawLine(New Pen(Color.Black, 2), P1, P3)
        Dim z1 As Single = 600 \ (single_Xe - single_Xa)
        For int_i = 0 To 600 Step z1
            g.DrawLine(New Pen(Color.AliceBlue, 1), int_i + z1, 0, int_i + z1, -600)
            g.DrawLine(New Pen(Color.Black, 2), int_i, 0, int_i, -10)
            g.DrawLine(New Pen(Color.Black, 1), int_i + z1 \ 2, 0, int_i + z1 \ 2, -5)
            g.DrawString(int_i \ z1 + single_Xa, New Font("Arial", 10), Brushes.Black, int_i - 5, 0)
        Next
        Dim z2 As Single = 600 \ (single_Ye - single_Ya)
 
        For int_i = 0 To -600 Step -z2
            g.DrawLine(New Pen(Color.AliceBlue, 1), 0, int_i - z2, 600, int_i - z2)
            g.DrawLine(New Pen(Color.Black, 2), 0, int_i, 10, int_i)
            g.DrawLine(New Pen(Color.Black, 1), 0, int_i - z2 \ 2, 5, int_i - z2 \ 2)
            g.DrawString(-(int_i \ z2 - single_Ya), New Font("Arial", 10), Brushes.Black, -20, int_i - 7)
        Next
 
        If single_Xa > x_Array(0) Then
            For int_i = 0 To UBound(x_Array) - 1 Step 1
                If x_Array(int_i) > single_Xa Then
                    If y_Array(int_i) > -single_Ye Then
                        If y_Array(int_i) < single_Ye Then
                            g.DrawLine(int_color, x_Array(int_i) * z1 - z1 * single_Xa, -y_Array(int_i) * z2 + z2 * single_Ya, x_Array(int_i + 1) * z1 - z1 * single_Xa, -y_Array(int_i + 1) * z2 + z2 * single_Ya)
                        End If
                    End If
                End If
            Next
        Else
            For int_i = 0 To UBound(x_Array) - 1 Step 1
                If y_Array(int_i) > -single_Ye Then
                    If y_Array(int_i) < single_Ye Then
                        g.DrawLine(int_color, x_Array(int_i) * z1 - z1 * single_Xa, -y_Array(int_i) * z2 + z2 * single_Ya, x_Array(int_i + 1) * z1 - z1 * single_Xa, -y_Array(int_i + 1) * z2 + z2 * single_Ya)
                    End If
                End If
            Next
        End If
        PictureBox1.Image = bmp
        Return single_Xa
    End Function
 
End Class

-------------------------------------------------------------------------
FORM1

VB Code:

Public Class Form1
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim neu As New Form2
        neu.BringToFront()
        neu.Show()
 
    End Sub
 
    Private Sub ComboBox1_Selectedindexchanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
        Dim str As String = "Sinus"
        Select Case str
            Case "Sinus"
                Form2.main()
            Case "Tan"
       Form2.main1()
        End Select
 
    End Sub

It would be a help if you wrap you codes w/ vbcode tags.

[Highlight=VB]
'your code here
[/vbcode]

If it won't run then you are getting at least one error message. If you're getting an error message and you want us to help fix the error...

it doesnt actually have a specific error mssg.it only says that i have an invalid operation exeption.
if i replace only two values from x and y scale for example Xe and Ye..it still can run and the user can typ in the values..but if i make it 4 unknown values that are Xa ,Xe,Ya and Ye..it wont run anymore.