microsoft visual basic 2010: reloaded fourth edition chapter seven more on the repetition structure

Microsoft Visual Basic 2010: Reloaded Fourth Edition

Chapter SevenMore on the Repetition Structure

Objectives

After studying this chapter, you should be able to:

• Code a counter-controlled loop using the For…Next statement

• Nest repetition structures

• Calculate a periodic payment using the Financial.Pmt method

• Select the existing text in a text box

• Code the TextChanged event procedure for a text box

Microsoft Visual Basic 2010: Reloaded, Fourth Edition 2

Objectives (cont'd.)

• Code a list box’s SelectedValueChanged and SelectedIndexChanged event procedures

• Include a combo box in an interface

• Code the TextChanged event procedure for a combo box

• Store images in an image list control

• Display an image stored in an image list control


Microsoft Visual Basic 2010: Reloaded, Fourth Edition

The For...Next Statement

• For...Next statement: processes a set of instructions a known number of times– Is a pretest loop

• Counter-controlled loop: a loop whose processing is controlled by a counter

• Counter variable: used to keep track of the number of times the loop has been processed

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

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The For...Next Statement (cont'd.)

• A negative stepvalue causes the loop counter to count down

• Decrementing: adding increments of a negative number

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

• Values for the counter variable, startvalue, stepvalue, and endvalue are shown within the hexagon

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Figure 7-1: How to use the For…Next statement


Figure 7-1: How to use the For…Next statement (cont’d.)



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Figure 7-2: Processing steps for Example 1 in Figure 7-1



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Figure 7-2: Processing steps for Example 1 in Figure 7-1 (cont’d.)


Figure 7-3: Problem specification for the Savings Account application



Figure 7-4: Sample run of the Savings Account application



Figure 7-5: Pseudocode and flowchart for the Calculate button’s Click event procedure


Figure 7-6: Calculate button’s Click event procedure



• Can use For…Next or Do…Loop for a counter-controlled loop

• With Do…Loop, you must:– Declare and initialize the counter variable– Update the counter variable– Include an appropriate comparison in the Do clause

• For…Next statement handles the declaration, initialization, update, and comparison tasks– Is more convenient to use



Figure 7-7: Comparison of the For…Next and Do…Loop statements


Nested Repetition Structures

• Repetition structures can be nested– Can use pretest or posttest loops for outer loop and

for inner (nested) loop

• A clock with minute and second hands demonstrates nested loops– Minute hand moves 1 position, then the second hand

moves 60 positions



Figure 7-8: Three versions of the logic used by a clock’s minute and second hands

Nested Repetition Structures (cont’d.)


Figure 7-9: Modified problem specification for the Savings Account application

Figure 7-9: Sample run of the Savings Account application

Nested Repetition Structures (cont’d.)


Figure 7-11: Two versions of the Calculate button’s Click event procedure


Figure 7-11: Two versions of the Calculate button’s Click event procedure (cont’d.)

The Payment Calculator Application


Figure 7-12: Problem specification for the Payment Calculator application

The Payment Calculator Application (cont’d.)


Figure 7-13: Sample run of the Payment Calculator application


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.)

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Figure 7-14: How to use the Financial.Pmt method

The Financial.Pmt Method (cont’d.)


Figure 7-15: Pseudocode and code for the Calculate button’s Click event procedure


Figure 7-15: Pseudocode and code for the Calculate button’s Click event procedure

Selecting the Existing Text in a Text Box

• SelectAll method: selects all text in a text box for replacement typing– User only needs to type the new value

• Enter event: occurs when the text box receives the focus– When the user tabs to the control– When the user uses the control’s access key– When the Focus method sends the focus to the

control– When the user clicks in the text box


Selecting the Existing Text in a Text Box (cont'd.)


Figure 7-16: How to use the SelectAll method


Figure 7-17: Loan text box’s Enter event procedure



Figure 7-18: Result of processing the text box’s Enter event procedure



• Entering a new value in the Loan text box does not update the monthly payments until the user clicks the Calculate button– May cause confusion


Figure 7-19: New loan amount entered in the Loan text box

Coding the 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


Figure 7-20: New principal entered in the Principal text box


Figure 7-21: Result of processing the text box’s TextChanged event procedure

Coding the TextChanged Event Procedure (cont’d.)

Coding the SelectedValueChanged and SelectedIndexChanged Event

Procedures


Figure 7-22: The list box’s SelectedValueChanged and SelectedIndexChanged event procedures

Including a Combo Box in an Interface

• Combo Box control:– Similar to a list box with a list of choices– List portion may be hidden– May contain a text field that allows the user to type an

entry that is not on the list

• Three styles of combo boxes, controlled by the DropDownStyle property:– Simple– DropDown (the default)– DropDownList


Using a Combo Box in an Interface


Figure 7-23: Examples of the three styles of combo boxes


Figure 7-24: Code used to fill the combo boxes in Figure 7-23 with values

Using a Combo Box in an Interface (cont'd.)

• Items.Add method: used to add items to a combo box

• 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)

• Items.count property: used to obtain the number of items in the combo box

• Sorted property: used to sort the items in the list

38Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Using a Combo Box in an Interface (cont'd.)

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Figure 7-25: Sample run of the Payment Calculator application using a combo box


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Figure 7-26: Code for the Payment Calculator application shown in Figure 7-25Microsoft Visual Basic 2010: Reloaded, Fourth Edition

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Figure 7-26: Code for the Payment Calculator application shown in Figure 7-25 (cont’d.)Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Using an Image List Control

• Image List control: – Stores a collection of images– Does not appear on the form; appears in the

component tray

• Add images to the control using the Images Collection Editor window


Using an Image List Control (cont’d.)

Figure 7-27: Image Viewer application



Figure 7-28: How to add images to an image list control’s Images collection



Figure 7-29: Completed Images Collection Editor window in the Image Viewer application



Figure 7-30: How to refer to an image in the Images collection



Figure 7-31: Sample run of the Image Viewer application



Figure 7-32: Code entered in the View button’s Click event procedure


• Creating the Slot Machine Application

Programming Tutorial 1

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Figure 7-34: MainForm in the Slot Machine application


• Creating the Birmingham Sales Application

Programming Tutorial 2

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Figure 7-40: MainForm for the Birmingham Sales application


Programming Example

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• Raise Calculator Application

Figure 7-46: MainForm for the Raise Calculator application


Summary

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

• A variable declared in a For clause has block scope

• Use a hexagon in a flowchart for a For…Next loop• Financial.Pmt method: calculates a periodic

payment on a loan or investment• SelectAll method: highlights text in a text box• TextChanged event: occurs when a control’s text

changes


Summary (cont'd.)

• 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

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

• Use SelectedItem, SelectedIndex, or Text property of a combo box to set the default item in a combo

• Combo box’s Items.Count property: used to obtain the number of items listed in the combo box


Summary (cont'd.)

• Combo box’s Sorted property: used to sort items listed in a combo box

• Combo box’s SelectedItem property: contains the value of the item selected in the list portion of the combo box

• Combo box’s Text property: contains the value that appears in the text portion of the combo box

• Combo box’s TextChanged event: occurs when the user either selects an item in the list portion or types a value in the text portion


Summary (cont'd.)

• Image list control: stores a set of images in its Images collection

• Images in an image list control belong to the Images collection

• Access an image in the Images collection using the Item property with the index of the desired image

• Image collection’s Count property contains the number of images in the collection

• Use a picture box control to display an image contained in an image list control


microsoft visual basic 2010: reloaded fourth edition chapter seven more on the repetition structure

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