Practical ProgrammingCOMP153-06S

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 (20th)

• 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)

• http://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 /

100ElseIf (IncomeTextBox.Text <= 60000) Then TaxLabel.Text = 7410 + (IncomeTextBox.Text –

38000) * 33 / 100Else TaxLabel.Text = 7410 + 7260 +

(IncomeTextBox.Text - 60000) * 39 / 100End 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