1. Practical Programming COMP153-06S Lecture 3: Making Decisions

2. Administration We are doing Lab 2 –MSDN available from CS office –Labs and Lectures are available in the lab and on the web –Try to finish by Friday (20 th ) You should have had Lab 1 verified by today, or at least by the end of this week

3. Programming So Far First: Controls, Properties, Events Second: Types and Arithmetic The test tutorial had a simple calculator which would have been more useful if we could have supplied an operation as well as 2 numbers. That is today’s topic.

4. Today – Making Decisions Computer can compare and branch In VB.NET –The If statement –The Select Case statement New type – Boolean (true or false) –Eg: enabled, visible properties The checkbox control allows people to make decisions – message box for popping up a window

5. The If statement If condition Then statements ElseIf condition Then statements Else statements End If Condition: either a Boolean property or a comparision (with and / or / not) Statements: any VB.NET statements

6. Eg: Setting background If condition Then statements Else statements End If If (YellowCheckBox.Checked) Then ActiveForm.BackColor = Color.Yellow Else ActiveForm.BackColor = SystemColors.Control End If

7. Calculator If (TextBox3.Text = "+") Then Label4.Text = Str(Val(TextBox1.Text) + Val(TextBox2.Text)) ElseIf (TextBox3.Text = "-") Then Label4.Text = Str(Val(TextBox1.Text) - Val(TextBox2.Text)) ElseIf (etc.) End If

8. Tax rates

9. Tax rates (2) http://www.ird.govt.nz/income-tax-individual/itaxsalaryandwage- incometaxrates.htmlhttp://www.ird.govt.nz/income-tax-individual/itaxsalaryandwage- incometaxrates.html Up to $38,000 19.5 cents/dollar 38,001 – 60,000 33 cents/dollar Over 60,000 45 cents/dollar If (IncomeTextBox.Text <= 38000) Then TaxLabel.Text = IncomeTextBox.Text * 19.5 / 100 ElseIf (IncomeTextBox.Text <= 60000) Then TaxLabel.Text = 7410 + (IncomeTextBox.Text – 38000) * 33 / 100 Else TaxLabel.Text = 7410 + 7260 + (IncomeTextBox.Text - 60000) * 39 / 100 End If Comparison with strings is sort order

10. The Select Case statement Select Case expression Case value statements Case value statements Case Else statements End Select

11. Fruit prices

12. Fruit prices (2) Select Case ItemTextBox.Text Case 1 PriceLabel.Text = WeightTextBox.Text * 3.99 Case 2 PriceLabel.Text = WeightTextBox.Text * 5.5 Case 3 PriceLabel.Text = WeightTextBox.Text * 6.0 Case Else MessageBox.Show(“Please Enter 1, 2 or 3”) End Select

13. Calculator (2) Select Case (TextBox3.Text) Case "+" Label4.Text = Str(Val(TextBox1.Text) + Val(TextBox2.Text)) Case "-" Label4.Text = Str(Val(TextBox1.Text) - Val(TextBox2.Text)) Case “*” Label4.Text = Str(Val(TextBox1.Text) * Val(TextBox2.Text)) Case “/” Label4.Text = Str(Val(TextBox1.Text) / Val(TextBox2.Text)) Case “^” Label4.Text = Str(Val(TextBox1.Text) ^ Val(TextBox2.Text)) Case Else Label4.Text = “You must use on of (*,+,-,/,^)” End Select

14. Case is clever (first variable) Case 1, 3, 5 Case 1 To 10 Case 1 To 4, 7 To 9, 11, 13 Dim Number As Integer = 8 Select Number ' Evaluate Number. Case 1 To 5 ' Number between 1 and 5, inclusive. MessageBox.Show("Between 1 and 5") Case 6, 7, 8 ' Number between 6 and 8. MessageBox.Show("Between 6 and 8") Case 9 To 10 ' Number is 9 or 10. MessageBox.Show("Greater than 8") Case Else ' Other values. MessageBox.Show("Not between 1 and 10") End Select

15. THE END of the lecture