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1
Lesson 2 Forms and Decisions

• Microsoft Visual Basic .NET, Introduction to
  Programming

2
Objectives

• Customize the look and feel of a form.
• Create forms that react to user events like
  clicking a button and pressing a key.
• Learn to use the OpenFileDialog box.
• Understand and use the various data types.
• Use variables and pass information from one part
  of the project to another.

3
Objectives

• Use the If statement in program code to make
  decisions.
• Use logical expressions and relational operators.
• Use GroupBoxes to arrange RadioButtons on a form.
• Use the TabIndex property to control the order in
  which controls receive focus.
• Import graphics to a form.

4
Vocabulary

• Accelerator key
• Assignment statement
• Boundary condition
• CInt() function
• Class level
• Concatenation operator
• Condition
• Constant
• Data type

• Dialog box
• End statement
• File filter
• If statement
• InputBox function
• IntelliSense
• InterCap
• Keywords
• Loads

5
Vocabulary

• Pixels
• Program flow
• Relational operators
• Run-time error
• Scope

• Strings
• Syntax
• TabIndex property
• Unicode
• Variable

6
Questions a Programmer Should Ask

• What is the best way to present the application?
• What are the needs of the users? (What do they
  need to see to do their job?)
• How are the users accustomed to seeing the
  information?
• What colors or objects will help them best
  utilize the application?

7
The Programming Code

• Start program
• Declare the variables you will use to make
  calculations
• Initialize values
• Get the data
• Process the data
• Show or save the information
• End program

8
Tip

• Note the indentation of the code in the code
  block. Indentation is used to make programming
  code easier for you to read. It has no
  significance to how Visual Basic reads it,
  although many languages now automatically indent
  code as you enter it. As you go forward with this
  text, pay attention to the indentation used in
  the Step-by-Step exercises.

9
View Code Button in the Solution Explorer Window
10
Tip

• Visual Basic makes code easy to follow by
  color-coding various parts of the code. This
  helps visually organize the code and makes
  debugging easier.

11
Default Anchoring
12
Tip

• If you want to enter code for a different
  object, use the Class Name and Method Name list
  boxes at the top of the Code window to open the
  objects Code window.

13
Note

• The keyword Public means that the method has no
  access restrictions within this form. The Sub
  keyword is an abbreviation for the word
  subprocedure (block of code). Sub is followed by
  the name of the control, for example, cmdExit, an
  underscore (_), the name of the current event,
  for example, Click, and parentheses.

14
Creating Simple Forms

• Start a Visual Basic Windows Application, which
  creates a new Windows form.
• Change the form properties (like the Text
  property) as needed.
• Add controls such as text boxes, labels, and
  buttons.
• Change the properties of the controls to convey
  information to the user.
• Add code to the objects methods (event
  procedures).

15
Pixels

• Visual Studio programmers use pixels when
  describing size and location information. Pixel
  stands for picture element. Together your monitor
  and the graphics card installed on your computer
  determine the number of pixels on your screen.
  Typical screen resolutions are 640 by 480 and 800
  by 600. The numbers refer to the number of
  columns of pixels by the number of rows of
  pixels. The more columns and rows, the higher the
  resolution of the picture. Higher resolution
  gives more detail in a smaller area.

16
Historically Speaking

• In the late 1950s and early 1960s, computer
  scientists developed ways to write programs that
  would interpret specialized programming languages
  into machine language. These programs are known
  as compilers. Before compilers, programs were
  either hard-wired into the machine or the machine
  was programmed directly with machine language.
  With the advent of compilers, programming
  languages were developed that were far easier for
  humans to understand.

17
Some Things to Consider

• What other forms will be open when this form
  opens?
• Will the user be able to use the other forms?
• Would it be more convenient to allow the user to
  see the other forms?
• Should the user's attention be focused solely on
  one form?

18
Tip

• You can select multiple controls on the form in
  Design mode by holding down the Ctrl key as you
  click each control. Then you can reposition all
  the controls at the same time. You may also
  select multiple controls on the form by selecting
  the Pointer tool in the Toolbox and clicking and
  dragging a box around the controls. A
  Step-by-Step exercise later in this lesson
  explores this technique.

19
Assignment Statements

• Many properties are also set by program code
  while the program is running. To set an objects
  property value while code is running, use an
  assignment statement. The assignment statement as
  it applies to objects and their properties has
  the following syntax
• object.Property Value

20
Tip

• One of the most important things programmers can
  do is document their code. Internal documentation
  is the easiest way of accomplishing this.
  Internal documentation is called commenting. If
  you place an apostrophe ( ', also called a single
  quote) at the beginning of a line, Visual Basic
  ignores the whole line and you can use it as a
  comment. As mentioned earlier, Visual Basic
  color-codes the code. It displays comments in
  green.

21
Windows Form Designer-Generated Code

• It appears in a neutral color with a plus symbol
  to the left. Click the plus symbol to expand the
  entry if it is not already expanded. Once
  expanded, you see code automatically generated as
  you add controls to the form and set the
  controls properties. This code should not be
  altered in the Code Editor. It should only be
  altered by adding new controls to the form and by
  changing properties values in the Properties
  window.

22
OpenFileDialog1

• OpenFileDialog1.DefaultExt "txt"
• OpenFileDialog1.InitialDirectory "c\My
  Documents"
• OpenFileDialog1.Filter "Text files .txt"
• OpenFileDialog1.ShowDialog()

23
IntelliSense

• As you enter a statement, a pop-up window
  appears with information about the statements
  syntax. This very useful feature is called
  IntelliSense. IntelliSense will complete words
  for you or just describe the structure of the
  statement and the options available to complete
  the statement.

24
The Open Dialog Box
25
Did You Know?

• FORTRAN and COBOL were two of the first
  high-level or third-generation languages created.
  FORTRAN was created for use by engineers and
  scientists. COBOL was created for the business
  world. Updated versions of both of these
  languages are still in use today.

26
The RadioButtonCheckBox Form
27
Computer Ethics

• Unauthorized copying of software is stealing. It
  is illegal in many countries, and people and
  corporations have been prosecuted for
  "bootlegging" software.
• Microsoft regularly shuts down illegal auctions
  on Ebay.

28
Variables

• A variable is a temporary storage location for
  data used in your application. Each variable has
  a name and a data type. The data type of a
  variable determines what kind of value it
  represents. The value of each variable, as the
  name implies, varies depending on different
  situations. For example, you can assign user
  input from a text box to a variable and use it to
  do calculations. Using variables like this also
  makes your code more efficient because data
  stored as a variable can be processed many times
  faster than data stored in the property of an
  object.

29
Constants

• The value of a constant remains the same.
  Constants are useful if you have a value that is
  used over and over or if the code contains a
  number that is difficult to remember, such as the
  value of pi. The use of constants makes it easier
  to read the code and also maintain the code.

30
Note

• When showing the syntax of a statement, items in
  the square brackets are optional. Items in
  italics stand for things that must be replaced
  with specific instances of the item. Words not in
  italics and not in square brackets are required
  parts of the statement. Often, in syntax
  statements, two-word descriptions, like data
  type, are combined to form a single word
  datatype. The IntelliSense help statements that
  appear in the Code Editor use this style to
  illustrate the syntax of statements.

31
Integer Data Type

• 4 bytes
• -2,147,483,648 to 2,147,483,647

32
Double Data Type

• double-precision floating-point
• 8 bytes
• -1.79769313486231E308 to -4.94065645841247E-324
  for negative values
• 4.94065645841247E-324 to 1.79769313486232E308 for
  positive values

33
Naming Variables and Constants

• Typically, you should select a name that is
  meaningful but not too long. It is helpful if you
  start the variable name with a three-letter
  prefix that identifies the data type for
  example, str for String data type and int for
  Integer data type. You cannot include spaces in
  the names of your variables or constants.
  Capitalize the first letter of each word in the
  variable name. This naming convention is called
  the InterCap method of naming variables and
  constants.

34
Building Programming Skills

• Before you write the code, it is helpful to
  write on paper what it is you want your
  application to accomplish. First, write English
  sentences that describe the process of solving
  the problem. Then, change the sentences into
  short statements that use some of the commands
  you will be using, but do not worry about syntax.

35
Step-by-Step 2.5, Step 6

• Dim strUserName As String
• strUserName InputBox("Please enter your
  full name.")
• Dim intAge As Integer 21
• Dim sglGPA As Single 3.65
• Dim CrLf As String Chr(13) Chr(10)
• lblGreeting.text "Welcome " strUserName "."
  _
• CrLf "Your age " intAge _
• CrLf "Your GPA " sglGPA

36
Gathering User Information Form
37
Concatenation Operator

• This operator joins strings together end to end.

38
Underscore Character

• The underscore character is the statement
  continuation character. There is no strict limit
  to the length of a line of code, but it is hard
  to read lines that extend beyond the edge of the
  screen. The solution to the problem is to break
  long lines of code into shorter lines without
  ending the statement. The underscore character at
  the end of a line indicates that the statement is
  continued on the next line. To use the underscore
  character, it must be the last character in the
  line and there must be a space before the
  character.

39
The Scope of Variables and Constants

• The scope of variables and constants describes
  the lifetime of a variable and indicates what
  parts of the program are aware of each variable
  or constant.

40
Hint

• There are many sites on the Internet that offer
  free and inexpensive controls that you can add to
  your Visual Basic applications. Before creating
  your own controls, you may want to see what is
  already available. There is no sense in
  reinventing the wheel.

41
Making Decisions

• If condition Then
• Statements if condition is True
• Else
• Statements if condition is False
• End If
• If condition Then
• Statements if condition is True
• End If

42
Step-By-Step 2.6

• Const AgeLimit As Integer 12
• Dim Age As Integer
• Age CInt(InputBox("Enter your age"))
• If Age lt AgeLimit Then
• MessageBox.Show("Your age is under the
  limit!")
• Else
• MessageBox.Show("You are too old.")
• End If

43
Note

• You may want to add the Debug toolbar to your
  normal toolbar display. Among many other buttons,
  the Debug toolbar has two buttons to run a
  program a triangle icon to start the program
  with the Debugger and an exclamation point icon
  that starts the program without the debugger. The
  square icon on the Debug toolbar stops program
  execution. To add the Debug toolbar, right-click
  the toolbar area and click Debug.

44
Important

• Using an equal sign as a relational operator is
  not the same as using the equal sign as the
  assignment operator. Used as the assignment
  operator, the value of the expression to the
  right of the equal sign is evaluated and assigned
  to the variable to the left of the equal sign.

45
Group Boxes

• Use group boxes to organize controls on a form.
  A group box visually separates groups of related
  text boxes, radio buttons, check boxes, labels,
  and buttons. Radio buttons have a special
  relationship to group boxes (formerly called
  frames) because only one radio button of a list
  of radio buttons contained in a group box can be
  selected. Independent groups of radio buttons are
  contained in separate group boxes.

46
Text Boxes

• One important way for the user to enter data is
  the text box. A text box appears on the form as a
  rectangle. The user enters data into the text box
  with the keyboard using all the editing tools
  familiar to anyone who works with Microsoft
  Windows programs.

47
Note

• While double-clicking a control to add it to a
  form, it is possible to add an unintended extra
  copy of the control. To remove a control from a
  form, select it by clicking anywhere within the
  control's boundary and press the Delete key.

48
The Annual Depreciation Form Showing Placement of
Controls
49
The AutoSize Property

• The AutoSize property of the Label control can
  be set by selecting its current value in the
  Properties window and entering a new value with
  the keyboard. Double-clicking the name of a
  property sometimes toggles the value of the
  property between different possible values. In
  this case, the value toggles between the two
  possible values of the AutoSize property True
  and False.

50
TabIndex Property

• When the program is run, the control with the
  TabIndex property of 0 starts with the focus.
  When the user presses the Tab key, focus shifts
  to the control whose TabIndex property is next in
  the sequence. The value of the TabIndex property
  for each control is set automatically while
  controls are created. Altering the TabIndex
  property during the design process lets the
  programmer control the order in which controls
  receive focus.

51
Step-by-Step 2.7

• Dim PurchasePrice As Decimal
• Dim SalvageValue As Decimal
• Dim Years As Integer
• Dim Depreciation As Decimal
• If rdbPriceOne.Checked True Then
• PurchasePrice 2500
• End If

52
Step-by-Step 2.7

• If rdbPriceTwo.Checked True Then
• PurchasePrice 4500
• End If
• If rdbSalvageOne.Checked True Then
• SalvageValue 200
• Else
• SalvageValue 400
• End If
• Years CInt(txtYears.Text)
• Depreciation (PurchasePrice - SalvageValue) /
  Years
• lblDepreciation.Text Depreciation.ToString()

53
TextBox Controls Clear Method

• To clear the contents of the text box, use the
  TextBoxs Clear method. This built-in method
  clears the contents of the Text property of the
  TextBox control, preparing the text box for more
  data entered by the user. A typical statement to
  clear a text box is txtYears.Clear(). Such a
  statement is usually called from a button on the
  form.

54
Summary

• Objects such as labels and text boxes are added
  to a form to give instructions or information to
  the user or to retrieve information from the
  user.
• The Property window allows you to change an
  object's property settings. The color, text, font
  type and size, and object size as well as an
  objects behavior are changed with Property
  settings. Properties of objects can also be
  changed at run time with program code.
• Many properties use True or False settings to
  determine their status at run time. These
  settings can also be altered later with program
  code.
• Program code is what actually gives instructions
  to the computer to perform calculations, move
  objects, change properties, and print reports. In
  Visual Basic, program code is typically
  associated with an object and is triggered by
  user events.

55
Summary

• The size and location of forms is set by the
  programmer. Pixels are the common unit of
  measurement used. A pixel, or picture element, is
  the smallest color dot supported by the system.
  The Size property of an object is set by the
  Height and Width subproperties of the object,
  while the Location property is set by the X and Y
  subproperties.
• Variables and constants must be declared before
  using them. A local variable is declared by using
  the Dim statement. Declare constants by using the
  Const statement.
• Variables and constants have set lifetimes or
  scope. The scope is determined by where the
  variable or constant is declared. The scope of a
  variable is its lifetime and visibility.

56
Summary

• Internal documentation is used in the program
  code to explain why something was done. Internal
  documentation is important for both the original
  programmer and the person who may have to make
  alterations to the program later.
• Assignment statements are program code used to
  assign values to variables or properties of
  objects while the program is running.
• A class is a template used to create an object.
  Everything in Visual Basic is created from a
  class.
• The OpenFileDialog control is a temporary dialog
  box used to get a filename from the user. Once
  collected, the filename can be used to open the
  file.  

57
Summary

• Radio buttons allow the user to select from a
  list of options. Only one radio button in a group
  may be selected. Read the status of a RadioButton
  control by accessing its Checked property.
• Check boxes allow the user to select multiple
  items from a list of options. Read the status of
  a CheckBox control by accessing its Checked
  property.
• The Dim (Dimension) statement declares a
  variable. Declaring a variable reserves space in
  memory for the value of the variable and
  associates a name and a data type with the
  variable.
• Variables are objects and, once declared, many
  methods are available to manipulate the value of
  the variable.

58
Summary

• Use the InterCap method to name variables and
  constants.
• The If statement is used to control program flow.
  Statements are executed (or not) based on the
  evaluation of a condition.
• Group boxes are used to group controls like radio
  buttons together.
• Text boxes are used to collect input from the
  user. The text box is a fixed part of a form,
  while the InputBox function shows a temporary
  dialog box to collect input from the user.
• A number of objects, including forms, buttons,
  and picture boxes, can display graphics.