Microsoft Visual Basic 2010 Reloaded Fourth Edition Chapter
Microsoft Visual Basic 2010: Reloaded Fourth Edition Chapter Seven More 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 Text. Changed event procedure for a text box Microsoft Visual Basic 2010: Reloaded, Fourth Edition 2
Objectives (cont'd. ) • Code a list box’s Selected. Value. Changed and Selected. Index. Changed event procedures • Include a combo box in an interface • Code the Text. Changed 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 3
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 Microsoft Visual Basic 2010: Reloaded, Fourth Edition 4
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 Microsoft Visual Basic 2010: Reloaded, Fourth Edition 5
Figure 7 -1: How to use the For…Next statement Microsoft Visual Basic 2010: Reloaded, Fourth Edition 6
Figure 7 -1: How to use the For…Next statement (cont’d. ) Microsoft Visual Basic 2010: Reloaded, Fourth Edition 7
The For. . . Next Statement (cont'd. ) Figure 7 -2: Processing steps for Example 1 in Figure 7 -1 Microsoft Visual Basic 2010: Reloaded, Fourth Edition 8
The For. . . Next Statement (cont'd. ) Figure 7 -2: Processing steps for Example 1 in Figure 7 -1 (cont’d. ) Microsoft Visual Basic 2010: Reloaded, Fourth Edition 9
The For. . . Next Statement (cont'd. ) Figure 7 -3: Problem specification for the Savings Account application Microsoft Visual Basic 2010: Reloaded, Fourth Edition 10
The For. . . Next Statement (cont'd. ) Figure 7 -4: Sample run of the Savings Account application Microsoft Visual Basic 2010: Reloaded, Fourth Edition 11
Figure 7 -5: Pseudocode and flowchart for the Calculate button’s Click event procedure Microsoft Visual Basic 2010: Reloaded, Fourth Edition 12
The For. . . Next Statement (cont'd. ) Figure 7 -6: Calculate button’s Click event procedure Microsoft Visual Basic 2010: Reloaded, Fourth Edition 13
The For. . . Next Statement (cont'd. ) • Can use For…Next or Do…Loop for a countercontrolled 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 Microsoft Visual Basic 2010: Reloaded, Fourth Edition
The For. . . Next Statement (cont'd. ) Figure 7 -7: Comparison of the For…Next and Do…Loop statements Microsoft Visual Basic 2010: Reloaded, Fourth Edition 15
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 Microsoft Visual Basic 2010: Reloaded, Fourth Edition
Figure 7 -8: Three versions of the logic used by a clock’s minute and second hands Microsoft Visual Basic 2010: Reloaded, Fourth Edition
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 Microsoft Visual Basic 2010: Reloaded, Fourth Edition
Nested Repetition Structures (cont’d. ) Figure 7 -11: Two versions of the Calculate button’s Click event procedure Microsoft Visual Basic 2010: Reloaded, Fourth Edition
Figure 7 -11: Two versions of the Calculate button’s Click event procedure (cont’d. ) Microsoft Visual Basic 2010: Reloaded, Fourth Edition
The Payment Calculator Application Figure 7 -12: Problem specification for the Payment Calculator application Microsoft Visual Basic 2010: Reloaded, Fourth Edition
The Payment Calculator Application (cont’d. ) Figure 7 -13: Sample run of the Payment Calculator application Microsoft Visual Basic 2010: Reloaded, Fourth Edition
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. ) Microsoft Visual Basic 2010: Reloaded, Fourth Edition 23
Figure 7 -14: How to use the Financial. Pmt method Microsoft Visual Basic 2010: Reloaded, Fourth Edition 24
The Financial. Pmt Method (cont’d. ) Figure 7 -15: Pseudocode and code for the Calculate button’s Click event procedure Microsoft Visual Basic 2010: Reloaded, Fourth Edition
Figure 7 -15: Pseudocode and code for the Calculate button’s Click event procedure Microsoft Visual Basic 2010: Reloaded, Fourth Edition
Selecting the Existing Text in a Text Box • Select. All 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 Microsoft Visual Basic 2010: Reloaded, Fourth Edition 27
Selecting the Existing Text in a Text Box (cont'd. ) Figure 7 -16: How to use the Select. All method Microsoft Visual Basic 2010: Reloaded, Fourth Edition 28
Selecting the Existing Text in a Text Box (cont'd. ) Figure 7 -17: Loan text box’s Enter event procedure Microsoft Visual Basic 2010: Reloaded, Fourth Edition 29
Selecting the Existing Text in a Text Box (cont'd. ) Figure 7 -18: Result of processing the text box’s Enter event procedure Microsoft Visual Basic 2010: Reloaded, Fourth Edition 30
Selecting the Existing Text in a Text Box (cont'd. ) • 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 Microsoft Visual Basic 2010: Reloaded, Fourth Edition 31
Coding the Text. Changed Event Procedure • Text. Changed 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 Microsoft Visual Basic 2010: Reloaded, Fourth Edition 32
Coding the Text. Changed Event Procedure (cont’d. ) Figure 7 -21: Result of processing the text box’s Text. Changed event procedure Microsoft Visual Basic 2010: Reloaded, Fourth Edition 33
Coding the Selected. Value. Changed and Selected. Index. Changed Event Procedures Figure 7 -22: The list box’s Selected. Value. Changed and Selected. Index. Changed event procedures Microsoft Visual Basic 2010: Reloaded, Fourth Edition 34
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 Drop. Down. Style property: – Simple – Drop. Down (the default) – Drop. Down. List Microsoft Visual Basic 2010: Reloaded, Fourth Edition 35
Using a Combo Box in an Interface Figure 7 -23: Examples of the three styles of combo boxes Microsoft Visual Basic 2010: Reloaded, Fourth Edition 36
Figure 7 -24: Code used to fill the combo boxes in Figure 7 -23 with values Microsoft Visual Basic 2010: Reloaded, Fourth Edition 37
Using a Combo Box in an Interface (cont'd. ) • Items. Add method: used to add items to a combo box • Selected. Item 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 Microsoft Visual Basic 2010: Reloaded, Fourth Edition 38
Using a Combo Box in an Interface (cont'd. ) Figure 7 -25: Sample run of the Payment Calculator application using a combo box Microsoft Visual Basic 2010: Reloaded, Fourth Edition 39
Figure 7 -26: Code for the Payment Calculator application shown in Figure 7 -25 Microsoft Visual Basic 2010: Reloaded, Fourth Edition 40
Figure 7 -26: Code for the Payment Calculator application shown in Figure 7 -25 (cont’d. ) Microsoft Visual Basic 2010: Reloaded, Fourth Edition 41
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 Microsoft Visual Basic 2010: Reloaded, Fourth Edition
Using an Image List Control (cont’d. ) Figure 7 -27: Image Viewer application Microsoft Visual Basic 2010: Reloaded, Fourth Edition
Using an Image List Control (cont’d. ) Figure 7 -28: How to add images to an image list control’s Images collection Microsoft Visual Basic 2010: Reloaded, Fourth Edition
Using an Image List Control (cont’d. ) Figure 7 -29: Completed Images Collection Editor window in the Image Viewer application Microsoft Visual Basic 2010: Reloaded, Fourth Edition
Using an Image List Control (cont’d. ) Figure 7 -30: How to refer to an image in the Images collection Microsoft Visual Basic 2010: Reloaded, Fourth Edition
Using an Image List Control (cont’d. ) Figure 7 -31: Sample run of the Image Viewer application Microsoft Visual Basic 2010: Reloaded, Fourth Edition
Using an Image List Control (cont’d. ) Figure 7 -32: Code entered in the View button’s Click event procedure Microsoft Visual Basic 2010: Reloaded, Fourth Edition
Programming Tutorial 1 • Creating the Slot Machine Application Figure 7 -34: Main. Form in the Slot Machine application Microsoft Visual Basic 2010: Reloaded, Fourth Edition 49
Programming Tutorial 2 • Creating the Birmingham Sales Application Figure 7 -40: Main. Form for the Birmingham Sales application Microsoft Visual Basic 2010: Reloaded, Fourth Edition 50
Programming Example • Raise Calculator Application Figure 7 -46: Main. Form for the Raise Calculator application Microsoft Visual Basic 2010: Reloaded, Fourth Edition 51
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 • Select. All method: highlights text in a text box • Text. Changed event: occurs when a control’s text changes Microsoft Visual Basic 2010: Reloaded, Fourth Edition 52
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, Drop. Down, and Drop. Down. List • Combo box’s Items. Add method: adds an item to the list • Use Selected. Item, Selected. Index, 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 Microsoft Visual Basic 2010: Reloaded, Fourth Edition 53
Summary (cont'd. ) • Combo box’s Sorted property: used to sort items listed in a combo box • Combo box’s Selected. Item 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 Text. Changed event: occurs when the user either selects an item in the list portion or types a value in the text portion Microsoft Visual Basic 2010: Reloaded, Fourth Edition 54
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 55
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