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Practical Programming COMP153-06S Lecture 3: Making Decisions
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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
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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.
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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
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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
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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
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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
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Tax rates
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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
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The Select Case statement Select Case expression Case value statements Case value statements Case Else statements End Select
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Fruit prices
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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
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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
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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
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THE END of the lecture
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