microsoft visual basic 2005: reloaded - timlin · microsoft visual basic 2005: reloaded, second...

Microsoft Visual Basic 2005: Reloaded Second Edition

Chapter 5Repeating Program Instructions

Microsoft Visual Basic 2005: Reloaded, Second Edition 2

Objectives

After studying this chapter, you should be able to:• Include the repetition structure in pseudocode and in

a flowchart• Write a For...Next statement• Calculate a periodic payment using the

Financial.Pmt method• Include a list box and a combo box in an interface• Write a Do...Loop statement


Objectives (continued)

• Initialize and update counters and accumulators• Display a dialog box using the InputBox function• Create a multiline text box that cannot be edited• Animate a control by moving it across a form• Have the computer sound a beep


The Repetition Structure

• Repetition structure (or loop): a structure that repeatedly processes one or more program instructions until a condition is met

• Pretest loop– The condition is evaluated before the instructions

within the loop are processed– The instructions may be processed 0 or more times

• Posttest loop– The condition is evaluated after the instructions within

the loop are processed– The instructions are always processed at least once


The Repetition Structure (continued)

• Repetition statements in Visual Basic– For...Next– Do...Loop– For Each...Next


The For...Next Statement

• For...Next statement– Processes a set of instructions a known number of

times– Is a pretest loop


The For...Next Statement (continued)



• Startvalue, endvalue, and stepvalue items– Control the number of times the loop is processed– Must evaluate to numeric values– Can be positive or negative

• A negative stepvalue causes the loop counter to count down

• Flowchart symbol for the For...Next loop is a hexagon


The Financial.Pmt Method

• Financial.Pmt method– Calculates a periodic payment on a loan or investment– Returns the periodic payment as a Double type value

• Rate and number of periods arguments must be expressed in the same units (monthly, annual, etc.)

• Also calculates the amount that must be saved each period to accumulate a specific sum


The Financial.Pmt Method (continued)


The Monthly Payment Calculator Application


The Monthly Payment Calculator Application (continued)


Selecting the Existing Text in a Text Box

• Windows standard: highlight the existing text when a text box receives the focus

• SelectAll method: selects all text in a text box• Enter event: occurs when the text box receives the

focus


Selecting the Existing Text in a Text Box (continued)


Coding a Control’s TextChanged Event Procedure

• TextChanged event– Occurs when a change is made in a control’s Text

property– Change may be made by user or the program


Coding a Control’s TextChanged Event Procedure (continued)


Using a List Box in an Interface

• ListBox tool: creates a ListBox control• ListBox control: displays a list of choices from

which the user can select 0 or more choices• SelectionMode property: controls the number of

choices a user can select– None: user can scroll but not select anything– One: user can select one item– MultiSimple and MultiExtended: user can select

multiple items


Using a List Box in an Interface (continued)


Adding Items to a List Box

• Items collection: a collection of the items in a list box

• Collection: a group of one or more individual objects treated as one unit

• Index: – A unique number that identifies an item in a collection– Is zero-relative: the first item has index of 0

• Add method: adds an item to the list box’s Items collection


Adding Items to a List Box (continued)



• Sorted property: – Determines if the list box items are sorted – Sort order is dictionary order


The SelectedItem and SelectedIndex Properties

• SelectedItem property: – Contains the value of the selected item in the list– If nothing is selected, it contains the empty string

• SelectedIndex property: – Contains the index of the selected item in the list– If nothing is selected, it contains the value -1

• Default list box item: the item that is selected by default when the interface first appears


The SelectedItem and SelectedIndex Properties (continued)


The SelectedValueChanged and SelectedIndexChanged Events

• SelectedValueChanged and SelectedIndexChanged events: occur when a user selects an item in a list box


The SelectedValueChanged and SelectedIndexChanged Events

(continued)


Modifying the Monthly Payment Calculator Application


Modifying the Monthly Payment Calculator Application (continued)


Using a Combo Box in an Interface

• ComboBox tool: creates a combo box control• ComboBox control:

– Similar to a list box– May contain a text field that allows the user to type an

entry that is not on the list– List portion may be hidden

• Three styles of combo boxes:– Simple– DropDown– DropDownList


Using a Combo Box in an Interface (continued)



• SelectedItem property: contains the value of the selected item in the list

• Text property: contains the value that appears in the text portion of the control (item selected or typed in)


The Do...Loop Statement

• Do...Loop statement: codes both a pretest or a posttest loop

• Use While or Until to code the condition for the loop• Repetition symbol in a flowchart is the diamond


The Do...Loop Statement (continued)


Using Counters and Accumulators

• Counter: a numeric variable used for counting• Accumulator: a numeric variable used for

accumulating• Initializing: assigning a beginning value to a

variable• Updating (or incrementing): adding a number to

the value of a variable• Counters are always incremented by a constant

value, usually 1


The InputBox Function

• InputBox function: displays a predefined dialog box– Contains a text message, an OK button, a Cancel

button, and an input area• Function: a predefined procedure that performs a

specific task and returns a value• InputBox function returns:

– The user’s entry if the user clicks the OK button– An empty string if the user clicks the Cancel button

or the Close button on the title bar


The InputBox Function (continued)


The Sales Express Application


The Sales Express Application (continued)


Programming Tutorial


Programming Example


Summary

• Repetition structure (or loop): repeatedly processes a set of instructions

• Pretest loop tests the condition before the instructions are processed

• Posttest loop tests the condition after the instructions are processed

• For...Next statement: a pretest loop that will process the instructions a fixed number of times

• Financial.Pmt method: calculates a periodic payment on a loan or investment


Summary (continued)

• SelectAll method: highlights text in a text box• TextChanged Event: occurs when a control’s text

changes• List box’s Items collection: adds an item to the list• SelectedItem property of a list box: contains the

value of the selected item in the list• SelectedIndex property of a list box: contains the

index position of the selected item in the list


Summary (continued)

• Combo box: similar to a list box but may not expose the list items until clicked

• Three styles of combo boxes: Simple, DropDown, and DropDownList

• Do...Loop statement: codes a pretest or posttest loop

• Use a While or Until condition in a Do...Loop• Flowchart symbol for repetition is a diamond


Summary (continued)

• Counter and accumulators: variables that calculate subtotals, totals, and averages

• InputBox function: allows user input• Console.Beep method: plays the sound of a beep

through the computer’s console speakers

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