Repeating Program Instructions

Objectives 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 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 9/19/2018 VB 2005

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 9/19/2018 VB 2005

The Repetition Structure (continued) Repetition statements in Visual Basic For...Next Do...Loop For Each...Next 9/19/2018 VB 2005

The For...Next Statement For...Next statement Processes a set of instructions a known number of times Is a pretest loop Syntax: For counter [As datatype]=startvalue to endvalue [stepvalue] [statements] Next counter 9/19/2018 VB 2005

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 9/19/2018 VB 2005

The For...Next Statement (continued) 9/19/2018 VB 2005

The For...Next Statement (continued) 9/19/2018 VB 2005

The Financial.Pmt Method Syntax: Financial.Pmt(Rate, NPer, PV[,Fv, Due]) 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 9/19/2018 VB 2005

The Financial.Pmt Method (continued) 9/19/2018 VB 2005

The Monthly Payment Calculator Application 9/19/2018 VB 2005

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 Syntax: textbok.selectAll() Enter event: occurs when the text box receives the focus 9/19/2018 VB 2005

Coding a Control’s TextChanged Event Procedure Occurs when a change is made in a control’s Text property Change may be made by user or the program 9/19/2018 VB 2005

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 9/19/2018 VB 2005

Using a List Box in an Interface (continued) 9/19/2018 VB 2005

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 9/19/2018 VB 2005

Adding Items to a List Box (continued) 9/19/2018 VB 2005

Adding Items to a List Box (continued) 9/19/2018 VB 2005

Adding Items to a List Box (continued) Sorted property: Determines if the list box items are sorted Sort order is dictionary order 9/19/2018 VB 2005

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 9/19/2018 VB 2005

The SelectedValueChanged and SelectedIndexChanged Events SelectedValueChanged and SelectedIndexChanged events: occur when a user selects an item in a list box 9/19/2018 VB 2005

The SelectedValueChanged and SelectedIndexChanged Events (continued) 9/19/2018 VB 2005

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 9/19/2018 VB 2005

Using a Combo Box in an Interface (continued) 9/19/2018 VB 2005

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) 9/19/2018 VB 2005

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 Syntax: Do While condition Do Statement(s) Statement(S) Loop Loop Until condition 9/19/2018 VB 2005

The Do...Loop Statement (continued) 9/19/2018 VB 2005

The Do...Loop Statement (continued) 9/19/2018 VB 2005

The Do...Loop Statement (continued) 9/19/2018 VB 2005

The Do...Loop Statement (continued) 9/19/2018 VB 2005

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 9/19/2018 VB 2005

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 Syntax: InputBox(Prompt [,title], [Defaultresponse]) 9/19/2018 VB 2005

The InputBox Function (continued) 9/19/2018 VB 2005

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 9/19/2018 VB 2005

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 9/19/2018 VB 2005

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 9/19/2018 VB 2005

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 9/19/2018 VB 2005