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Practical Programming COMP153-06S

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 )

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Practical Programming COMP153-06S

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  1. Practical ProgrammingCOMP153-06S 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 (20th) • 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.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

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