repeating program instructions chapter microsoft visual basic.net: reloaded 1

Repeating Program Instructions

Chapter Microsoft Visual Basic .NET: Reloaded

1

2Microsoft Visual Basic .NET: Reloaded

Objectives

• Include the repetition structure in pseudocode and in a flowchart

• Write a For…Next statement• Calculate a periodic payment using the Pmt

function• Write a Do…Loop statement• Initialize and update counters and

accumulators• Display a dialog box using the InputBox

function


The Repetition Structure

• Repetition Structure (also known as a loop)• Repeatedly processes a set of instructions

until a condition is met

• Pretest loop:• Evaluation occurs before instructions within loop

• PostTest loop:• Evaluation occurs after the instructions within

loop are processed • Instructions will always be processed at least

once


The For…Next Statement

• Use to code a loop to process instructions a precise number of times

• For…Next is a pretest loop• StartValue (starting value of loop counter)

• EndValue (ending value of loop counter)

• Stepvalue (amount of change of loop counter)• Default stepvalue is a positive 1• Can be negative• Designate with Step keyword

• Example Step -2• Subtracts 2 from the loop counter


HOW TO…


The For…Next Statement (continued)


The Pmt Function

• Use to calculate a periodic payment on a loan or investment

• Contains 5 arguments

• Rate, Nper, PV are required

• FV, Due are optional

• Negation operator reverses the sign of a number

• -Pmt(.05,3,9000)


HOW TO…


The Payment Calculator Application


The Payment Calculator Application (continued)


The Do…Loop Statement

• Can be used to code both pretest and posttest loops• Do While or Do Until is a pretest loop

• Pretest loops should have a “priming read”• Data input entry placed above loop

• Loop While or Loop Until is a posttest loop• [While|Until] portion can only contain one of

the keywords (While or Until)• While processes instructions as long as the

condition evaluates true• Until processes instructions until the condition

becomes true


HOW TO…


The Do…Loop Statement (continued)


Using Counters and Accumulators

• Counter – numeric variable used for counting something number of employees paid in a week

• Accumulator – numeric variable used for calculating running totals total dollar amount of weeks payroll

• Initializing – assigning a beginning value to a variable

• Updating (incrementing) – adding a number to the value stored in the counter or accumulator


The Sales Express Application

• Application for sales manager to display average amount the company sold during the prior year.

• Sales manager will enter each salesperson’s sales

• Application will use a counter to keep track of number of sales amounts and an accumulator to total those amounts


The Sales Express Application (continued)


The InputBox Function

• Displays a dialog box that prompts the user in input information

• Contains a prompt, one or more buttons, and an input area for data entry

• Prompt - message you want displayed• Title displays caption of input box• defaultResponse - initial text displayed in the

input area• Ok button returns value in input area, Cancel

and Close buttons return empty string


The InputBox Function (continued)


Code for the Sales Express Application


Programming Example – Grade Calculator

• Application allows the user to enter the points a student earns on 4 projects and 2 tests

• Totals the points earned and calculates grade• Total Points Earned Grade

360-400 A

320-359 B

280-319 C

240-279 D

below 240 F

• Displays total points and grade earned


TOE Chart


User Interface


Objects, Properties, and Settings


Objects, Properties, and Settings (continued)


Tab Order


PseudoCode

btnExit Click event procedure

Close application

btnAssignGrade Click event procedure

1. repeat while the number of projects counter is less than 5

if the points earned is numeric

add the project points to the total points accumulator

add 1 to the number of projects counter

else

display an appropriate message in a message box

end if

end repeat

(continued on next slide)


PseudoCode (continued)2. repeat while the number of tests counter is less than 3

get the points earned on the test

if the points earned is numeric

add the test points to the total points accumulator

add 1 to the number of tests counter

else

display an appropriate message in a message box

end if

end repeat

(continued on next page)


PseudoCode (continued)3. Assign the grade based on the total points earned value:

>= 360 assign A as the grade

>= 320 assign B as the grade

>= 280 assign C as the grade

>= 240 assign D as the grade

<240 assign F as the grade

4. Display the total points earned in lblTotalPoints

5. Display the grade in lblGrade


Code


Code (continued)


Summary

• Three programming structures are sequence, selection, and repetition

• Repetition (loop) allows program to repeatedly process one or more program instructions

• Pretest loops test before program instructions

• Posttest loops test after program instructions and will always be processed at least once

• Pmt function calculates payment on a loan


Summary (continued)

• The condition in a loop evaluates to a Boolean variable

• While processes loop instructions while the condition is true

• Until processes loop instructions until the condition becomes true

• Use a counter or accumulator to calculate subtotals, totals and averages

• Counters and accumulators must be initialized and updated


Summary (continued)

• InputBox Function displays a dialog box that displays a message, an OK button, a Cancel button, and an input area.

• Test for possible division by zero to prevent an error ending the program prematurely

repeating program instructions chapter microsoft visual basic.net: reloaded 1

Documents

loop loop

loop counter slide

loop posttest loop

true slide

doloop statement

fornext statement

inputbox function slide

pretest loop startvalue