Practical Programming COMP153-08S Lecture: Repetition

Programming So Far First: Controls, Properties, Events Second: Types and Arithmetic Third: Variables (Global/Local) Fourth: Decisions If and Select This week: Repetition

Repetition Making things happen more than once This is what computers are good at –Doing simple repeated tasks 1.The user can repeat commands 2. The computer can repeat

Computer Repeating Can use Timer controls –Useful when you want things to repeat slowly – eg: graphics, animation Can use looping statements –When you simply want to get a task done as quickly as possible –Easier to program than timers

Timer Control – Digital Clock

Timer dissected Set Timer controls first: Timer1.enabled = True Timer1.Interval = 1000 (1 second) Label1.Text = TimeString( ) (code for timer) –Get current time from system clock as a string. Can change the interval to see the timer control more explicitly

An Aside - Graphics Top left is (0,0) x-axis increases left to right y-axis increases top to bottom (x,y) is a pixel position

Timer Examples Adding to a counter Moving a control

Timer code Import picture set SizeMode PictureBox1.Left = PictureBox1.Left + 2 If PictureBox1.Left > Me.Width - PictureBox1.Width Then PictureBox1.Left = 0 End If

Bouncing lily Dim GoingRight As Boolean Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load Timer1.Enabled = True Timer1.Interval = 1 GoingRight = True End Sub Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick If GoingRight Then PictureBox1.Left = PictureBox1.Left + 2 If PictureBox1.Left > ActiveForm.Width - PictureBox1.Width Then GoingRight = False End If Else PictureBox1.Left = PictureBox1.Left - 2 If PictureBox1.Left = 0 Then GoingRight = True End If End Sub

Repetition statements The For / Next statement For x = 1 To 5... Next Note: the variable x must be declared (Dim x as Integer).

Moving Image without timer Dim x As Integer For x = 1 To 5 PictureBox1.Left = PictureBox1.Left + 2 MessageBox.Show(x) Next

Creating new forms dynamically When you want to copy the form you have designed as your program runs –Dim two As Form1 –two = new Form1() and –two.Show()

Example Another example Dim x as Integer Dim f as Form1 For x = 100 To 200 Step 30 f = New Form1() f.Width = x f.Show() Next

THE END of the lecture