Graphics exercise1

Public Class Form1

    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        Dim myGraphics As Graphics = PictureBox1.CreateGraphics
        Dim myPen0 As New Pen(Color.Blue, 5)
        Dim myPen1 As New Pen(Color.Gray, 0.5) : Dim myPen2 As New Pen(Color.Red, 2)
        Dim a, id As Integer
        Dim x1, y1, angle As Single
        myGraphics.Clear(Me.BackColor)
        myGraphics.DrawRectangle(myPen0, x1, y1, 499, 499)
        a = 150
        For id = 0 To 500 Step 50
            myGraphics.DrawLine(myPen1, id, 0, id, 500)
            myGraphics.DrawLine(myPen1, 0, id, 500, id)
        Next
        myGraphics.TranslateTransform(500 / 2, 500 / 2)

        If TextBox1.Text >= 250 Then
            MsgBox("The Largest Radius should be less than 500")
            TextBox1.Clear()
            Return
        End If


        For a = TextBox1.Text / 5 To TextBox1.Text Step TextBox1.Text / 5


            For id = 0 To 360 Step 2
                angle = id * Math.PI / 180
                x1 = a * Math.Cos(angle) : y1 = a * Math.Sin(angle)
                myGraphics.DrawRectangle(myPen2, x1, y1, 1, 1)
            Next id
        Next


        myGraphics.Dispose()
    End Sub
    Private Sub Form1_Load(sender As Object, e As System.EventArgs) Handles Me.Load
        Me.AutoSize = True
        PictureBox1.Top = 0 : PictureBox1.Left = 0
        PictureBox1.Width = 500 : PictureBox1.Height = 500
        Button1.Left = PictureBox1.Width + 50 : Button1.Top = 150
        Label1.Left = PictureBox1.Width + 50 : Label1.Top = 140

    End Sub
End Class