Program design example

1. Program design example Task: Develop an algorithm expressed in pseudocode for a specified problem

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. Problem specification 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) Back toNotes

11. 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 Define inputs and outputs Back toNotes

12. 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

13. Describe how the methods will work initialize totalShares,perSharePrice, perShareDiv, and userChoice to invalid values while the program is running display the available operations and prompt the user to choose one get the user’s choice perform the requested operation or display an error message if the choice is invalid Back toNotes Structurechart

14. set invalid:userChoice, perSharePrice,perShareDiv, totalShares whileprogram is running switchuserChoice display menu, prompt get userChoice displayprice, div updateprice, div updatebalance error--choice initializebalance displaybalance Structure chart ReinvestmentAccount Pseudocode

15. 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

16. get the user’s choice read user choice into userChoice Back toparent

17. perform the requested operation or display an error message if the choice is invalid if userChoice is 1, initialize account balance if userChoice is 2, display current balance if userChoice is 3, display current share info if userChoice is 4, update share info if userChoice is 5, update balance if userChoice is 6, skip (do nothing) otherwise, print “Invalid choice.” Back toparent

18. initialize account balance print “Enter initial number of shares:” read user choice into totalShares Back toparent

19. display current balance print “Current number of shares is ”, totalShares if totalShares is valid if perSharePrice is valid print “Current market value is ”, totalShares perSharePrice else print “Per share price has not been entered” else print “Initial number of shares has not been entered” Back toparent

20. display current share info if perSharePrice is valid print “Current price per share is ”, perSharePrice else print “Per share price has not been entered” if perShareDiv is valid print “Current dividend rate is ”, perShareDiv else print “Dividend rate has not been entered” if perSharePrice is valid print “Current price per share is ”, perSharePrice else print “Per share price has not been entered” if perShareDiv is valid print “Current dividend rate is ”, perShareDiv else print “Dividend rate has not been entered” Back toparent

21. update share info print “Enter price per share:” read user input into perSharePrice print “Enter dividend rate:” read user input into perShareDiv Back toparent

22. update balance if totalShares is valid if perSharePrice is valid if perShareDiv is valid add totalShares perShareDiv  perSharePriceto totalShares 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 toparent

23. 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

24. 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

25. 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.