Program Design and Development

1. Program Design and Development

2. Steps In Program Development • Define the Problem • Inputs, outputs, processes • Outline the solution • Major steps • Major subtasks • Major control structures (repetition loops) • Major variables • Mainline Logic

3. Steps in PD Continued • Develop Algorithm • Using pseudocode and flowcharts • Test Algorithm • Code into programming language • Run complier • Document and maintain the program

4. Types of Programming • Structured/Top Down Programming • Starting with solution and working into more complex details • Modular Design • Grouping tasks together by function • Structure Theorem • Elimination of GOTO, replacement with IF-THEN-ELSE

5. Algorithm Definition • Lists the steps involved in accomplishing a task • Written in simple english and not a formal document • An algorithm must be • Lucid, precise, and unambiguous • Give the correct solution in all cases • Eventually end

6. Pseudocode • Essentially it is structured english and formalized to look like high-level computer languages • Statements are written in simple english • Each instruction is written on a single line • Keywords and indentations are used to signify control structures • Each set of instructions is written from top to bottom with only one entry and one exit • Groups of statements may be formed into modules and that group given a name

7. Program Data • Variables, constants, and literals • Integer - 16 • Byte length - 8 • Short integer - 32 • Long integer - 64 • Real • Float – single precision • Double – double precision • Character • Boolean

8. Data Structures • Record • File • Array • String

9. Basic Computer Operations • A computer can receive information • “READ” and “GET” • A computer can put out information • “PRINT”, “WRITE”, “PUT”, “OUTPUT”, and “DISPLAY” • A computer can perform arithmetic actions • + for ADD • - for SUBTRACT • * for MULTIPLY • / for DIVIDE • () for PARENTHESES

10. Basic Computer Options Cont. • A computer can assign a value to a variable or memory • To give an initial value use “INITALISE” or “SET” • To assign a value use ‘=‘ • To keep a piece of information for later use ‘SAVE’ or ‘STORE’ • A computer can compare variables and select one of two alternative actions • Use of IT THEN and ELSE • Actually it can select multiple actions • A computer can repeat a group of actions • DOWHILE

11. The Structure Theorem • Sequence • The straightforward listing of each step • Selection • The presentation of a condition and the choice between two actions • Repetition • The presentation of a set of instructions to be performed repeatedly as long as a condition is true

12. Developing An Algorithm • Defining the Problem • Input • Output • Processing • Use Meaningful Name

13. Designing an Algorithm • Begin with a rough sketch of steps required to solve the problem • Use these requirements and structure theorem to establish how the processing will take place • It is important to not start coding until the necessary steps of defining the problem and designing the solution algorithm have been solved.

14. Checking an Algorithm • Choose simple input test case • Establish what the expected result should be • Make a table of relevant variable names • Walk through the test case • Continue the process until the algorithm is correct

15. Selection Control Structures • Used to illustrate a choice between two or more actions • Simple IF statement • Simple selection with null false branch (null ELSE statement) • Combined selection (IF/AND) • Nested IF Statement • Linear nested IF statement

16. The CASE Structure • Another way of expressing a linear nested IF statement • Can often appear cumbersome

17. Repetition Control Structures • Developed because many programs require the same logic to be repeated for several sets of data. • Example • DOWHILE condition p is true • Statement block • ENDO

18. DOWHILE Loop Processing • The logical condition p is tested • If condition p is found to be true, the statements listed in the statement block will be executed once. Control is returned to the retesting of condition p. • If condition p is found to be false, control passes to the next statement after ENDDO and no further processing takes place within the loop.

19. Two important DOWHILE considerations • Testing of the condition is done at the beginning of the loop. • The only way to terminate the loop is to render the DOWHILE consideration false.

20. REPEAT_UNTIL Structure • Is the exact opposite of the DOWHILE • Condition is checked at the end as opposed to the beginning • Counted repetition • Question—is any method better than another?

21. Time for Practice