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Objectives

• Create a structure
• Declare and manipulate a structure variable
• Differentiate between a structure variable and
  member variables
• Create an array of structure variables
• Include a radio button in an interface

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Objectives (continued)

• Include a check box in an interface
• Include a list box in an interface
• Code a text boxs KeyPress event
• Code a text boxs Enter event
• Associate a procedure with different events

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Structures

• You can create your own data types using the
  Structure statement
• Referred to as user-defined data types or
  structures
• Structures contain member variables between
  Structure clause and End Structure clause
• Member variables are declared using Public
  keyword followed by the variable name and then
  the desired data type

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HOW TO
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Using a Structure to Declare a Variable

• Variables declared using a structure are often
  referred to as structure variables

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HOW TO
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Passing a Structure Variable to a Procedure

• The personnel manager at Johnsons Lumber wants an
  application that he can use to save each
  managers employee number, name, and salary in a
  sequential access file
• Figure 10.4 shows a sample run of the Johnsons
  Lumber application
• Figure 10.5 shows how you can code the
  application without using a structure
• Figure 10.6 shows coding the application using an
  Employee structure to group together the employee
  data

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Passing a Structure Variable to a Procedure
(continued)
10
Passing a Structure Variable to a Procedure
(continued)
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Passing a Structure Variable to a Procedure
(continued)
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Passing a Structure Variable to a Procedure
(continued)
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Passing a Structure Variable to a Procedure
(continued)
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Passing a Structure Variable to a Procedure
(continued)
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Creating an Array of Structure Variables

• An array of structures can be used in place of
  two or more parallel arrays
• Figures 10.7 and 10.8 demonstrate using an array
  of structure variables for the Takoda Tapahe
  application first introduced in chapter 9

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Creating an Array of Structure Variables
(continued)
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Creating an Array of Structure Variables
(continued)
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Adding a Radio Button to the Form

• Use Radio Button Tool in the toolbox
• Radio Button allows you to limit user to only one
  choice in a group of two or more related and
  mutually exclusive choices.
• Radio buttons are placed in a group box control
  or panel control to be mutually exclusive
• Group box or panel control must be added to form
  before adding radio button
• Set default button within group by setting
  Checked property to True

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HOW TO
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Adding a Radio Button to the Form (continued)
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Adding a Radio Button to the Form (continued)
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Adding a Radio Button to the Form (continued)
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Adding a Check Box Control to the Form

• Check boxes allow user to select any number of
  choices from a group of one or more independent
  and nonexclusive choices

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Adding a Check Box Control to the Form (continued)
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Adding a Check Box Control to the Form (continued)
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Adding a Check Box Control to the Form (continued)
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Adding a List Box to an Interface

• Use a list box to display a list of choices from
  which the user can select zero, one, or more
  choices

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Adding a List Box to an Interface (continued)
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Adding Items to a List Box

• Items in a list box belong to Items Collection
• Collection is group of one or more individual
  objects treated as one unit
• Items in the collection identified by an index
• An index is a unique number determined by the
  items order of placement in the collection
  starting with zero
• Add method adds items to the list box
• The item selected when interface first appears is
  referred to as the default list box item

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HOW TO
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The SelectedItem and SelectedIndex Properties
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The SelectedItem and SelectedIndex Properties
(continued)
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The SelectedItem and SelectedIndex Properties
(continued)
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The SelectedItem and SelectedIndex Properties
(continued)
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Using the KeyPress Event

• A controls KeyPress event occurs when the user
  presses a key while the control has focus
• KeyPress event has two parameters sender and e
• Use e.KeyChar property to determine which key was
  pressed
• Use e.Handled property to cancel if key was
  inappropriate for desired action

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HOW TO
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Selecting the Existing Text in a Text Box

• Use SelectAll method in appropriate Sub such as
  the Enter event for text box
• Enter event occurs when user tabs to control and
  focus is received

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Associating a Procedure with Different Events

• List each event, separated by commas, in the
  Handles section of the procedure header

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Programming Example Glovers Application

• Glovers Industries stores the item numbers,
  wholesale prices, and retail prices of the items
  it sells in a sequential access file named
  items.txt.
• Opal Jacoby, the companys sales manager, wants
  an application that allows her to enter an item
  number and then display either the wholesale
  price or the retail price

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Programming Example Glovers Application
(continued)

• Data is stored in items.txt, one item per line
• Item number is first,
• then wholesale price, and
• then retail price

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TOE Chart
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User Interface
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Objects, Properties, and Settings
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Tab Order
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Pseudocode

• frmGlovers Load event procedure
• Try
• open items.txt for input
• repeat until no more characters to read or end
  of array
• read an item number, wholesale price, and
  retail price and
• assign it to the mitmItems array
• add the item number to the lstNumber control
• add 1 to the variable that keeps track of the
  array subscripts
• end repeat
• close the items.txt file
• select the first item in lstNumbers control
• Catch (use general catch statement to handle
  any errors)
• if error occurs, display exception description
  in a messagebox

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Pseudocode (continued)

• btnExit Click event procedure
• close application
• btnDisplay click Event procedure
• assign item number selected in lstNumbers to
  strSearchFornumber variable
• repeat until item number is located in mitmItems
  array
• add 1 to the variable that keeps track of array
  subscripts
• if radWholesale control is select
• display in lblPrice wholesale price stored in
  mitmItems array
• else
• display in lblPrice retail price stored in
  mitmItems array
• radRetail_Click, radWholesale_Click event
  procedures and
• lstNumbers.SelectedIndex Changed procedure
• clear the contents of the lblPrice control

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Code
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Code (continued)
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Code (continued)
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Summary

• You can use the Structure statement to define a
  user-defined data type (or structure) in Visual
  Basic .NET
• Typically enter the Structure statement in the
  forms Declarations section
• A structure variable contains one or more member
  variables
• You access a member variable using the structure
  variables name, followed by the dot member
  access operator and the member variables name

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Summary (continued)

• Use an assignment statement to assign a value to
  a member variable
• Data type of value must match data type of member
  variable
• Structure variable can be passed to procedures
• You access a member variable in an array element
  using the arrays name, followed by the elements
  subscript enclosed in parentheses, the dot member
  access operator, and the member variables name

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Summary (continued)

• Use radio buttons when you want to limit the user
  to one of two or more related and mutually
  exclusive choices
• Two is the minimum number of radio buttons in a
  group? recommended maximum is seven
• The label in the radio buttons Text property
  should be entered using sentence capitalization
• Assign a unique access key to each radio button
  in an interface

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Summary (continued)

• Use a group box control (or a panel control) to
  create separate groups of radio buttons
• Only one button in each group can be selected at
  any one time
• Designate a default radio button in each group of
  radio buttons
• Use check boxes when you want to allow the user
  to select any number of choices from a group of
  one or more independent and nonexclusive choices

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Summary (continued)

• A list box should display minimum of three
  selections and maximum of eight selections at a
  time
• Default item in list box should be either the
  most used selection or the first selection in the
  list
• You can use the e parameters KeyChar and Handled
  properties to prevent a text box from accepting
  inappropriate characters
• You can enter more than one event after the
  Handles keyword in a procedure