1 © 2000 John Urrutia. All rights reserved. Qbasic Constructing Qbasic Programs.

1© 2000 John Urrutia. All rights reserved.

Qbasic

Constructing Qbasic Programs


Program DevelopmentProblem definition – statement

Who – The person, group, organization

What – The record, file, system, data

When – The timeframe

Where – The location

Why – The business reason


Program DevelopmentProblem definition -

decompositionData

Input – what are the data sources.Output – what are the data sinks.

ProcessDetailed description of how the Input is

manipulated into Output.


Program DevelopmentProgram design – Algorithm

Sequence – linear execution of instructions

Selection – Identify a processing pathBinaryCase

Iteration – repetitive execution of instructions


Program DevelopmentProgram design – Flowcharts

A graphical representation of the problem definition

Process

Decision TerminationManual

Screen


Program DevelopmentProgram design – Pseudocode

An English-like representation of the problem definition

IF the meat is green Thenmove it to the waste bucket

Else

move it to the good bucket


Program DevelopmentImplementation – coding

The syntactical exercise of converting the program design into a specific programming language.


Program DevelopmentV&V –Verification & Validation

Specification errors

Syntax errors

Logic errors


Program DevelopmentDocumentation

Program - internal

User - external


B. A. S. I. C.Beginners

All-purpose

Symbolic

Instruction

Code

QBasic – QuickBASIC


Qbasic Character SetLetters:

a-z and A-Z

Digits:0-9

Blank:the space character ( )

Special characters:+ - * / \ = < > . , ’ ” ( ) : ; ^ _ $ # ? ! % &


Qbasic KeywordsA keyword has a predefined meaning

within Qbasic.Examples:

LET END REM PRINT


Qbasic Data TypesAll data in Qbasic is identified by a

data typeNumbers

% – Integer -32,768 to 32,767 & – Long integer

-2,147,483,648 to 2,147,483,647

! – Single precision 7 digit (1038)

# – Double precision 15 digit (10308)


Qbasic Data TypesStrings:

Any set of characters enclosed in double quotation marks.

“ ”Maximum of 14,656 Characters


Constants & VariablesConstants

“literal” values that cannot be changed

No label

VariablesValue can be changed

Referenced by a label


LabelsA name assigned to represent a

variable.Must start with a letter

Should be meaningful.

Can have periods imbedded.

Should carry the data type.


The LET statementAssigns a value to a variable.

Can be Explicit or Implicit

LET variable.Name = value

LET my.nbr! = 0

LET my.str$ = “This is my string”

LET tot! = tot! + purchases! + taxes!


The PRINT statementWrites information to the terminal.

PRINT output-list

PRINT X$

PRINT 5 + 7

PRINT “Hello World”

PRINT (prints a blank line)


The END statementEND terminates execution

Closes any open files.

Not required but highly recommended.


The CLS statementCLear Screen

Erases all characters from the terminal

Places cursor at position 0,0 (top left corner)


The REM statementThe REM ark statement

Treats everything to the right as a comment.

‘ – Is short hand for the REM


SPACE$(), SPC() and TAB()SPACE$(n)

Returns a string of n spaces

SPC(n) – skips n spaces

TAB(n) – specifies an exact column


The PRINT USING statementWrites formatted data to the teminal

PRINT USING “format-string” ; output-list

The format-string specifiesNumeric edited data formats

String formats

Literal data


USING format charactersStrings

\n\ – first n +2 characters in the string

! – first character in the string

& – no formatting

_ – print character not format


USING format charactersNumbers

# – number digit

. – decimal point

, – thousands separator

+ – sign of number

- – trailing minus sign

$ $$ – fixed / floating dollar sign

1 © 2000 John Urrutia. All rights reserved. Qbasic Constructing Qbasic Programs.

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