CHAPTER 6 - The Repetition Structure

Repetition structure

(or loop) Repeatedly processes instructions until condition is met

Looping condition

The requirement for repeating the instructions

Loop exit condition

The requirement for not repeating the instructions

Pretest loop

Evaluates condition prior to processing instructions

Posttest loop

Evaluates condition after processing instructions

Do...Loop statement

Used to code both pretest loop and posttest loop

Pretest, posttest

Two variations of syntax of do...loop: One for _______ loop and one for ________ loop

While keyword

Indicates that instructions should be processed while condition is true

Until keyword

Indicates that instructions should be processed until condition becomes true

Do...Loop statement

Begins with Do clause, ends with Loop clause Instructions to be repeated are placed between Do and Loop clauses

Condition

must evaluate to Boolean True or False

Do, loop

Location of { While | Until } condition

Pretest loop: Appears in __ clause

Posttest loop: Appears in ____ clause

Diamond

Represents loop condition in flowchart

Infinite loop

Also called endless loop. The condition to end the loop is never met

Stop debugging

To stop an infinite loop: Click Debug on the menu bar, then click ____ _________

Counters and Accumulators

Used to calculate subtotals, totals, and averages

Counter

Numeric variable used for counting

Accumulator

Numeric variable for accumulating (adding together) something

Initializing

Assigning beginning value

Updating

(incrementing) Adding a number to accumulator's value. Number can be positive or negative. Done within the loop body

Priming read

Use to prime (prepare or set up) loop by performing first action prior to entering loop

Update read

Allows user to update value that controls loop's condition

Arithmetic Assignment Operators

Used to abbreviate an assignment statement: Containing an arithmetic operator

For...Next statement

Used to code a counter-controlled loop. Processes instructions precise number of times. Condition tested before processing (pretest loop). Must specify start value, end value, and step value.

Looping range

Start value and end value provide _______ _____

Counter

Step value increments or decrements _______

Hexagon

For clause represented by a _______ in flowchart

Nested repetition structure

Inner loop placed entirely within outer loop. Inner loop is referred to as nested loop. Clocks use this structure to keep track of time

Refresh method

method, Ensures that computer processes any previous lines of code that affect interface appearance

Sleep method

method, Delays program execution

List box

object. Displays list of choices from which user can select zero or more choices

SelectionMode property

Controls number of choices that can be selected

ListBox tool

Used to add list box to interface

3-8

List box can be made any size you want. Windows standard: _-_ choices

Collection

Group of objects treated as one unit

Items collection

Refers to group of items in list box

Index

Unique number that identifies each item in collection. First item has index of zero

Add

Items collection's ___ method: Used to add item to list box. Usually entered in form's Load event procedure

Sorted property

______ ________ of list box: Determines order of displayed items. If True, newly added item is placed in its proper position. If False, newly added item is placed at end of list. Uses dictionary sort order

SelectedItem property

Contains value of selected item. Contains empty string when no item is selected

SelectedIndex property

Contains value of selected item's index . Contains -1 when no item is selected

Default list box item

Appears when application is first loaded. Chosen by setting either SelectedItem or SelectedIndex property

SelectedValueChanged event, SelectedIndexChanged event

Occur when user or code statement selects item in list box. Can use these events to process instructions when selection is made