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Lecture Summary for IT 236 on 6/20/06

Review Questions

1. What is a namespace?
   Ans: A namespace is a naming convention that organizes .NET items into related categories. Examples of namespaces are System, System.IO, System.Data, System.Xml.

2. What is the size of an Integer variable? What is its maximum range?
   Ans: 4 bytes; 2^31, which is approximately 2 billion.

3. What is the maximum length of a String?
   Ans: Over 2 billion bytes.

4. How do you make a text box read only?
   Ans: Set its ReadOnly property to True.

5. True or False: The name of an event handler looks like
   <NameOfControl>_<NameOfEvent>
   Ans: Strictly speaking false. Although this form of the event handler name is conventional, the name can be anything you wish. The Handles statement determines to which events the event handler responds.

6. Name three ways other than clicking on a button to invoke the event handler registered to that button.
   Ans: (1) Clicking the space bar when the button has the focus, (2) Clicking the Enter key when the button is set as the AcceptButton for the form, (3) Invoking the PerformClick method of the button in the code.

7. If x is defined as
   Dim x As Double = 0.005474
   write two format strings that will format x in these two ways:
   0.0055      .00548. Ans:
   "#0.0000"    "#.00000"

8. If x is defined as
   Dim x As Double = 4583938.57463
   write two format strings that will format x in these two ways:
   4,583,938.57      4583938. Ans:
   "#,##0.##" "#0."

9. Write a Windows application that will both increase the height and width of a clicked button by 10 pixels. Change the Height and Width properties of the button.
   Ans: If btnA is the name of the button, here is the event handler:
   Public Sub btnA_Click(ByVal sender As Object, _
   
   ByVal e As EventArgs) Handles btnA.Click

   btnA.Width = btnA.Width + 10
   btnA.Height = btnA.Height + 10
   

   End Sub

10. Where do you put code in a Windows application that must run before any user input occurs.
    Ans: In the Form1_Load event handler.

Colors In VB.NET

• To set the background color of an object x to red in code using the color name:
  x.BackColor = Color.Red

• Here is a table of VB.NET Color Names.

• To set the background color of an object x to red in code using the red, green and blue components:
  x.BackColor = Color.Argb(255, 0, 0)

Practice Problems

• Display "Life is like a box of chocolates." in txtBox in blue letters on a gold background.

  Ans: See the Chocolates example.

• Place three picture boxes picA, picB and picC on a form. Set the properties as specified in this table:

  Name	Left	Top	Width	Height	Color
  picA	20	20	200	200	White
  picA	40	40	160	160	Blue
  picA	20	60	60	120	Red

  Set the background color of the form to black.

  Ans: See the PictureBoxes example.

• Specify that at most two characters can be typed into the textbox txtStateAbbreviation.

Formatting Data

• The ToString method can accept a format string:
  WriteLine(x.ToString("#0.00"))

• Tables of Format Strings

• The WriteLine method can also accept a format string as its first argument. Any additional arguments, numbered as 0, 1, 2, ..., are substituted into the format string at the locations {0}, {1}, {2}, ... Here is an example:
  Dim x As Integer = 35
  Dim y As Double = 3.24
  Dim a As String = "abc"
  WriteLine("x = {0} y = {1,5:#0.00} a = {2}", x, y, a)

• Notes: {0} means use argument 0, which is x.
  {1,4:#0.00} means use argument 1, which is y, field width of 5 and a picture format of #0.00.

• The picture format #0.00 means always display first digit to the left of decimal point and display two digits to the right of the decimal point.
  {2} means use argument 2, which is a.

• A positive value for the field width means right justify within the field.

• A negative value for the field width means left justify within the field.

• See how the output is formatted in the Mortgage2 example.

Practice Problems

1. Write a Windows application that inputs an amount and outputs the tax on that amount. The tax is computed as 8% of the amount. Format the output.

   Ans: See the Tax example.

2. Write a Windows application that reads the number of credit hours, the total grade points (sum of A=4, B=3, etc times credit hours for each class). From this input information, compute the GPA and output the gpa, formatted to two digits behind the decimal point.

   Ans: See the Gpa1 example.

3. Write a Windows application that reads
   (a) The x-coordinate of Point 1,
   (b) The y-coordinate of Point 1,
   (c) The x-coordinate of Point 2,
   (d) The y-coordinate of Point 2.
   Output the distance between the two points, using the distance formula that you learned in high school geometry. Format the output.

   Ans: See the Pythagorean example.

Using a Message Box

• See the Input-MessageBox example.

• To display an input box, use the method InputBox. The arguments are Prompt, Title and DefaultResponse. The return value is the string that is input by the user.

• In the Input-MessageBox example, the input box is invoked in the Form1_Load event handler. This event handler fires when the form is first loaded.

• To display a message box, use the method MessageBox.Show. The arguments are OutputText, Caption, Buttons and Icon.

• The message box is invoked in the Form_Load event handler after the user clicks OK on the input box.

• To use MessageBox.Show in a console application, a reference to System.Windows.Forms must be added to the project.

Structured Programming in VB.NET

• Structured Programming in Everyday Life

• Structured programming means constructing a computer program using only sequence, repetition, or selection.

• Examples: DaysOfWeek1 (C)   DaysOfWeek2 (C)   TempDescriptors (W)

More Controls

• See the Controls example.

• CheckBox
  Properties:
  Checked:   A Boolean value. True means the checkbox is checked; False means it is unchecked.

  Text:   The CheckBox caption.

  Method:
  PerformClick:   Executes event handler for Click method.

  Event:
  CheckedChanged:   Fires when value of Checked propery changes from True to False or from False to True.

• GroupBox
  Properties:
  Text:   String

• RadioButton
  Properties, Methods, Events:   Same as for CheckBox with this exception: only one RadioButton control can have Value = True per group box.
• Example: Beverage (W)

• TrackBar
  Properties:
  Minimum:   The minimum possible value of the trackbar.

  Maximum:   The maximum possible value of the trackbar.

  LargeChange:   The change in the trackbar value when PageUp or PageDown are pressed.

  SmallChange:   The change in the trackbar value when the arrow keys are pressed.

  TickFrequency:   The distance between trackbar tick marks.

  Value:   The current value of the trackbar.

  Event:
  Scroll:   Fires when the thumb of the trackbar is moved.

Practice Problem

1. Write a Windows application with ScrollBar and PictureBox controls. Set the minimum and maximum values of the scroll bar to 0 and 255, respectively. When the scroll bar is moved from its minimum to maximum value, the background color of the picture box should change from red to pink to white. The various shades of the color pink can be obtained by the VB statement
   pinkShade = Color.FromArgb(255, x, x)
   where x is between 0 and 255 inclusive.

   Ans: See the Pink Example.

Private and Public Variables

• Private or Public Variables are declared outside of any method. Example:
  Private count As Integer
  Public count As Integer

• A Private variable is accessable anywhere in a class or module.

• Use a Private variable when the variable must retain its value to use in more than one method.

• A Public variable is accessable anywhere in the entire solution.

Practice Problems

1. Write a Windows application that inputs a sequence of numbers. Output the count of input numbers greater than 100. Describe the layout of your user interface and the event handlers that you need.

   Ans: See the Over90 example.

2. Write a Windows application that inputs sequentially the letter grade and credit hours for courses. Output the student's grade point average.

   Ans: See the Gpa2 example.

The CurrencyConverter Project

• Finish discussing the CurrencyConverter Project.