Repeating Program Instructions Chapter Microsoft Visual Basic.NET: Reloaded 1

2 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

3 Microsoft Visual Basic.NET: Reloaded 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

4 Microsoft Visual Basic.NET: Reloaded 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

5 Microsoft Visual Basic.NET: Reloaded HOW TO…

6 Microsoft Visual Basic.NET: Reloaded The For…Next Statement ( continued )

7 Microsoft Visual Basic.NET: Reloaded The For…Next Statement ( continued )

8 Microsoft Visual Basic.NET: Reloaded 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)

9 Microsoft Visual Basic.NET: Reloaded HOW TO…

10 Microsoft Visual Basic.NET: Reloaded The Payment Calculator Application

11 Microsoft Visual Basic.NET: Reloaded The Payment Calculator Application ( continued )

12 Microsoft Visual Basic.NET: Reloaded 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

13 Microsoft Visual Basic.NET: Reloaded HOW TO…

14 Microsoft Visual Basic.NET: Reloaded The Do…Loop Statement ( continued )

15 Microsoft Visual Basic.NET: Reloaded The Do…Loop Statement ( continued )

16 Microsoft Visual Basic.NET: Reloaded The Do…Loop Statement ( continued )

17 Microsoft Visual Basic.NET: Reloaded The Do…Loop Statement ( continued )

18 Microsoft Visual Basic.NET: Reloaded The Do…Loop Statement ( continued )

19 Microsoft Visual Basic.NET: Reloaded 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

20 Microsoft Visual Basic.NET: Reloaded 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

21 Microsoft Visual Basic.NET: Reloaded The Sales Express Application ( continued )

22 Microsoft Visual Basic.NET: Reloaded 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

23 Microsoft Visual Basic.NET: Reloaded The InputBox Function ( continued )

24 Microsoft Visual Basic.NET: Reloaded The InputBox Function ( continued )

25 Microsoft Visual Basic.NET: Reloaded Code for the Sales Express Application

26 Microsoft Visual Basic.NET: Reloaded 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 A B C D below 240F Displays total points and grade earned

27 Microsoft Visual Basic.NET: Reloaded TOE Chart

28 Microsoft Visual Basic.NET: Reloaded User Interface

29 Microsoft Visual Basic.NET: Reloaded Objects, Properties, and Settings

30 Microsoft Visual Basic.NET: Reloaded Objects, Properties, and Settings ( continued )

31 Microsoft Visual Basic.NET: Reloaded Tab Order

32 Microsoft Visual Basic.NET: Reloaded 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)

33 Microsoft Visual Basic.NET: Reloaded 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)

34 Microsoft Visual Basic.NET: Reloaded 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

35 Microsoft Visual Basic.NET: Reloaded Code

36 Microsoft Visual Basic.NET: Reloaded Code ( continued )

37 Microsoft Visual Basic.NET: Reloaded 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

38 Microsoft Visual Basic.NET: Reloaded 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

39 Microsoft Visual Basic.NET: Reloaded 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