Program Design and Development Steps In Program Development

Program Design and Development

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

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

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-THENELSE

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

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

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

Data Structures • Record • File • Array • String

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

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

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

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

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.

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

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

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

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

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.

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.

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?

Time for Practice