1 program design

8/6/2019 1 Program Design

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Program DesignProgram DesignDamairiawan Desta (32384)



ObjectiveObjective

y To describe the steps in the program

development process

y To introduce current program design

methodology

y To introduce procedural and object-

oriented programming

y To introduce algorithms and pseudocode

y To describe program data



7 Steps in Program Development7 Steps in Program Development

1. Define the problem

2. Outline the situation

3.Develop the outline into algorithm

4. Test the algorithm

5. Code the algorithm

6. Run the program7. Document and maintain the program



Program Design MethodProgram Design Method

y procedure-driven

y event-driven

y

data-driven.



ProcedureProcedure--driven program designdriven program design

y Based on the idea that the most

important feature of a program is 'what' it

does

y The details about the actual structure of

the data are not considered until all the

high-level processes or functions of the

program have been defined.



EventEvent--driven program designdriven program design

y Based on the idea that an event or

interaction with the outside world can

cause a program to change from one

known state to another.

y The initial state of a program is identified,

then all the triggers that represent valid

events for that state are established.



DataData--driven program designdriven program design

y Based on the idea that the data in a

program is more stable than the

processes involved.

y It begins with an analysis of the data and

the relationships between the data, in

order to determine the fundamental data

structures.



What is an algorithm? What is an algorithm?

y An algorithm is like a recipe: it lists the

steps involved in accomplishing a task.

y It can be defined in programming terms as

a set of detailed, unambiguous an ordered

instructions developed to describe the

processes necessary to produce the

desired output from a given inputy The algorithm is written in simple English



y An algorithm must:

be lucid, precise and unambiguous

give the correct solution in all cases

eventually end.



What is What is pseudocodepseudocode??

y Pseudocode is really structured English. It

is English that has been formalized an

abbreviated to look like high-level

computer languages.



y Statements are written in simple English.

y Each instruction is written on a separateline.

y Keywords and indentation are used tosignify particular control structures.

y Each set of instructions is written from

top to bottom, with only one entry andone exit.

y Groups of statements may be formed intomodules, and that group given a name.



Program dataProgram data

Three main discussion:

y Variables

Is the name given to a collection of memory cell,designed to store particular data item. The valuestored may change or vary as the program executes.

y Constants

Is a data item with a name and a value that remain thesame during the execution of the program.

y Literals Is a constant whose name is the writte representation

of its value.



Data TypesData Types

y Should be clearly defined at the beginning

of the program.

y Can be:

Elementary data items

Data structures



Elementary Data ItemElementary Data Item

y Contain single variable that is always

treated as a unit.

y Usually classified into data types.

y A data type consists of a set of data

values and a set of

y operation that can be performed on

those values.



The most common elementary data types:The most common elementary data types:

y Integer : representing a set of whole numbers,positive, negative or zero. e.g. 3, 576, -5

y Real : representing a set of numbers, positive ornegative, which may include values before or aftera decimal point. Sometimes referred to as floatingpoint numbers. e.g. 19.2, 1.92E+01, -0.01

y Character : representing the set of characters onthe keyboard, plus some special characters. e.g. ¶A·,

¶b·, ¶$·y Boolean : representing a control flag or switch,

which may contain one of only two possiblevalues; true or false.



Data StructuresData Structures

y Is an aggregate of other data items.

y Its component could be elementary data

items or another data structure.

y Data is grouped together in a particular

way to reflects the situation with which

the program is concerned.



The most common Data StructuresThe most common Data Structures

y Record: a collection of data items or fields that allbear some relationship to one another.

example: a student record; may contain the student¶snumber, name, address and enrolled subjects.

y File: a collection of records. example: a student file; may contain a collection of the

above student records.

y String: a collection of characters that can be fixed

or variable. Example: the string ´Si Bhe´may represent a student¶s

name.



y Array: a data structure that is made up of

a number of variables or data items that

all have the same data type and are

accessed by the same name. Example: an array called ¶scores· may contain a

collection of students¶ exam scores.

Access to the individual items in the array ismade by the use of an index or subscript

beside the name of the array scores[3]



FilesFiles

y A popular method of storing informationis to enter and store data on a file.

y The ma jor advantages of using files are:

Several different programs can access thesame data.

The data can be entered and reused severaltimes.

The data can be easily updated andmaintained.

The accuracy of the data is easier to enforce.



DataValidationDataValidation

y Data should always undergo a validation

check before it is processed by a

program.

y Different types of data require different

checks ² for example:



y Correct type: the input data should match the data type

definition stated at the beginning of the program.

y Correct range: the input should be within a required set

of values.

y Correct length: the input data should be the correct

length.

y Completeness: all required fields should be present.

y Correct date: an incoming data should be acceptable.

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