Program design example

Task: Develop an algorithm expressed in pseudocode for a specified problem

Program design steps

• Problem specification• Define inputs and outputs• Decompose into classes and methods• Describe how the methods will work• Convert method descriptions to code• Test the code

Problem specification

• Based on information from customer– job supervisor (employee)– client (independent consultant)– instructor (student)

• State what the program must do.• Specification is like a contract.• Summarize specification in Purpose section of

header comment.Exampleproblem

Define inputs and outputs

• Describe information input by user.• Describe results output to user.• Include descriptions in data dictionary:

– most inputs will correspond to variables– outputs may be variables or expressions– other items

• constants• transitional variables

Exampleproblem

Decompose into classes and methods

• Simple programs that perform a single task may be implemented with a single class containing a single method, main.

• When a design includes more than one class or method, each should be documented as to its specific purpose within the overall design.

Exampleproblem

Describe how the methods will work

• Show each method as a separate algorithm.• Algorithm design should be precise, but

should not include programming language details like type declarations and syntax.

• Use variable names.• Use pseudocode.• Indent to show program structure.

Exampleproblem

Convert method descriptions to code

• Choose appropriate types and declare constants, input and output variables, and transition variables.

• Converting pseudocode statements to Java statements should only involve changes to conform to Java syntax.

• Do not change the design while writing code.

Exampleproblem

Test the code

• Do not change the design when correcting code for compiler errors.

• Do not “poke and hope.” If you get a compiler error or incorrect output, first determine why you got the error.

• Choose test input that exercises each part of your program.

• If output is wrong, change the design.Exampleproblem

Reinvestment account

• Money invested in shares of stock may be maintained in a special reinvestment account.

• When dividends are paid, they are automatically used to purchase additional shares, which are added to the account.

• Dividends must be computed for original as well as reinvested shares.

Input/Output Pseudocode Structure chart Suggestions

Write a program to maintain a reinvestment account. The following operations must be implemented:– initialize the account balance– display the current balance (number of shares

and current market value)– display current price and dividend per share– update price and dividend information– update the balance (at current dividend rate)

Problem specification

Back toNotes

Define inputs and outputs

• Inputs– operation to be

performed– number of shares in

account– price per share– dividend rate per share

• Outputs– number of shares in

account– market value of

account– price per share– dividend rate per share

Back toNotes

Decompose into classes and methods

• A single class will be used, with a single method, main.

• An alternative approach, using multiple methods, would be to implement each of the required operations as an individual method.

Back toNotes

while the program is runningdisplay the available operations and prompt the user to choose oneget the user’s choiceperform the requested operation or display an error message if the choice is invalid

Describe how the methods will work

initialize totalShares, perSharePrice, perShareDiv, and userChoice to invalid values

Back toNotes

Structurechart

ReinvestmentAccount

set invalid:userChoice, perSharePrice,perShareDiv, totalShares

whileprogram is running

display menu, prompt

get userChoice switchuserChoice

Pseudocode

Structure chart

initializebalance

displaybalance

displayprice, div

updateprice, div

updatebalance

error--choice

display the available operations and prompt the user to choose one

print “Reinvestment account, available operations:”print “1. Initialize the account balance”print “2. Display the current balance (number of

shares and current market value)”print “3. Display current price and dividend per share”print “4. Update price and dividend information”print “5. Update the balance (at current dividend rate)”print “6. Quit the program”print “Enter desired operation:”

Back toparent

get the user’s choice

read user choice into userChoice

Back toparent

perform the requested operation or display an error message if the choice is invalid

if userChoice is 1, initialize account balanceif userChoice is 2, display current balance if userChoice is 3, display current share infoif userChoice is 4, update share infoif userChoice is 5, update balanceif userChoice is 6, skip (do nothing)otherwise, print “Invalid choice.”

Back toparent

initialize account balance

print “Enter initial number of shares:”read user choice into totalShares

Back toparent

print “Current market value is ”, totalShares perSharePrice

display current balance

print “Current number of shares is ”, totalShares

else print “Per share price has not been entered”else print “Initial number of shares has not been

entered”

if totalShares is valid

if perSharePrice is valid

Back toparent

if perSharePrice is validprint “Current price per share is ”, perSharePrice

else print “Per share price has not been entered” if perShareDiv is valid

print “Current dividend rate is ”, perShareDivelse print “Dividend rate has not been entered”

if perSharePrice is validprint “Current price per share is ”, perSharePrice

else print “Per share price has not been entered” if perShareDiv is valid

print “Current dividend rate is ”, perShareDivelse print “Dividend rate has not been entered”

display current share info

Back toparent

update share info

print “Enter price per share:”read user input into perSharePriceprint “Enter dividend rate:”read user input into perShareDiv

Back toparent

update balance

add totalShares perShareDiv perSharePrice to totalShares

if totalShares is validif perSharePrice is valid

if perShareDiv is valid

else print “Dividend rate has not been entered”else print “Per share price has not been entered”

else print “Initial number of shares has not been entered” Back to

parent

Convert method descriptions to code

• Define constants for:– valid menu choices (int)– invalid data value (double)– error messages (String)

• Use switch statement to implement menu• If you change the design, you must submit a

copy of the design with your changes along with your code

Back toNotes

Test the code

• Test all switch cases and selection branches, including those that display error messages

• Make sure numeric formulas produce correct results

• Make sure prompts and other elements of the user interface are coherent and understandable

Back toNotes

Suggestion Box

• Suggest at least one improvement to the user interface or program design.

• The best suggestions, if feasible, will be incorporated into future lab assignments. Particular consideration will be given to improvements involving the use of arrays.

• If there are no feasible suggestions, changes to the design dictated by the instructor may be assigned for future labs.