Practical Programming COMP153-06S Lecture 3: Making Decisions

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

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.

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

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

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

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

Tax rates

Tax rates (2) incometaxrates.htmlhttp:// incometaxrates.html Up to $38, cents/dollar 38,001 – 60, cents/dollar Over 60, cents/dollar If (IncomeTextBox.Text <= 38000) Then TaxLabel.Text = IncomeTextBox.Text * 19.5 / 100 ElseIf (IncomeTextBox.Text <= 60000) Then TaxLabel.Text = (IncomeTextBox.Text – 38000) * 33 / 100 Else TaxLabel.Text = (IncomeTextBox.Text ) * 39 / 100 End If Comparison with strings is sort order

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

Fruit prices

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

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

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

THE END of the lecture