Introduction to Qbasic - PowerPoint PPT Presentation

Introduction to Qbasic

Program Concepts

• as per Module 7 Study Book
• “Getting Started” p 4 - 15

Qbasic with an Introduction to Visual Basic by Schneider

• “Program Development Cycle” p 28 - 38 Qbasic with an Introduction to Visual Basic by Schneider

• Computer programs
• development cycle
• program planning
• planning tools
• variables
• rules for naming
• assigning values

Programming Languages:

What is a program?

It is software

A detailed set of instructions to execute a specific task

performs tasks in the IPOS cycle

1958 ALGOL

1960 LISP

1960 COBOL

1962 APL

1962 SIMULA

1964 BASIC

1964 PL/I

1966 ISWIM

1970 Prolog

1972 C

1975 Pascal

1975 Scheme

1977 OPS5

1978 CSP

1978 FP

1980 dBASE II

1983 Smalltalk-80

1983 Ada

1983 Parlog

1984 Standard ML

1986 C++

1986 CLP(R)

1986 Eiffel

1988 CLOS

1988 Mathematica

1988 Oberon

1990 Haskell

Cobol

C, C++

Fortran

Pascal

ADA

JAVA

HTML

According to Sammet, over 200 programming languages were developed between1952 and 1972, but she considered only about 13 of them to be significant.

• Program to compute gross amount due on an invoice
• multiply unit price by quantity of the purchase giving the gross amount

COBOL

* compute net amount due

IF discount-code = 0

move gross-amount to net-amount -due

ELSE

multiply .02 by gross-amount

giving discount-amount

subtract discount-amount from gross-amount

giving net-amount-due

* print net amount due

move net-amount-due to net-amount-due-out

write report-line-out from detail-line

after advancing 2 lines

C

/* Compute gross amount due

gross = price * qty-purch;

/* compute net amount due

if disc_code = 0

net=gross;

else

{

disc_amt = .02 * gross

net=gross-disc_amt

}

/* Print net amount due

printf{“The net amount due is %d/n”, net};

gross = price *qty

C compute gross net amount due

IF (code = 0 ) then

net = gross

ELSE

disc = .02 * gross

net = gross - disc

ENDIF

C Print net amount due

WRITE (CRTOUT.*) “The net amt due is $”,net

FORTRAN

gross.amount = unit.price * quantity.purch

REM compute net amount due

IF discount.code = 0 THEN

net.amount.due = gross.amount

ELSE

discount = .02* gross.amount

net.amount.due = gross.amount - discount

ENDIF

REM print net amt due

PRINT USING “the net amt due is$##,###.##”;net.amount.due

BASIC

COBOL

C

FORTRAN

BASIC

• Qbasic is part of DOS 5.0 or later
• Windows 3.11
• double click the Qbasic icon in Windows
• double click MSDOS icon in Windows; at the DOS prompt type “Qbasic” i.e. c:\qbasic
• Windows 95
• on master disc/CD-ROM
• others\oldmsdos\qbasic.exe

• Windows 98
• …tools\oldmsdos\qbasic.exe
• You can also download it from the Internet at

http://members.xoom.com/

white_acid/basic/compiler/

qbasic.zip

• K Block
• start; programs; dos applications; quickbasic
• Z Block
• shortcut

• ALT + enter to maximise screen
• Ctrl + break to stop a continuously looping program

• Menu Bar - drop down menus for functions

File Edit View Search Run Debug Options Help

• Title Bar - name of program currently being accessed; until initially saved is “Untitled”

------------------------ Untitled -------------------------

• View Window - window where program is written
• Immediate Window - used for debugging
• Status Bar - information on program

• access to drop down menus by:
• using mouse
• pressing ALT key highlights shortcut keys e.g. F, E, V etc. to menus; highlighted letters in menu are shortcuts
• ESC key to return to View Screen
• become familiar with contents of menus

Output

Process

Input

• determine outputs - what is the question?
• determineinputs - what is the user required to enter/ data available?
• determineprocess - algorithm / mathematical formulas

algorithm - step by step solution to the problem

• 5 steps in the planning process
• ????

• Analysis - define the program
• Design - plan the solution; consider all ‘what if scenarios’
• Code - translate into (QBasic) language
• Test and Debug
• DOCUMENTATION!!!!!

• Flowcharts
• Pseudocode
• Top-down charts

• represents the steps in the algorithm in a graphical manner

• Draw a flow chart that will take an angle entered in degrees, convert it to radians and calculate the sin, cos and tan of the angle.
• The syntax for sin cos and tan are not necessary. A flow chart is a description of the process and does not necessarily contain any “code”

• Uses English like phrases with some Qbasic terms to outline the program
• assign grades:

enter exam mark

if exam >=50 then grade is pass

else grade is fail

print grade

end

• Hierarchy chart
• show overall structure of program
• show organisation of program but omit the specific processing
• describe what each module does and how modules relate
• used for larger programs - Assignment 5
• may combine top down charts and flow charts

hours = 25

grosspay = payrate * hours

PRINT grosspay

END

• Quantities referred to by symbolic names
• make general solutions
• Variable name: is the name of a storage location in primary memory where Qbasic stores the value of the variable
• value can change during program execution

y = 10

z = x + y

total = z + x

y = total

x = 10

x = x+y

• may only contain letters, digits and full stop
• may not contain a blank space
• must start with a letter and may be up to 40 characters
• may NOT be a reserved word e.g let, print
• generally given a value of 0 initially but...

4sale

Test1

Rumplestiltskin

%Interest

Gross Pay

Grosspay

GroSSPay

Valid

invalid

valid

valid

invalid

invalid

valid

valid

• Draw a flowchart that take two times in hours, minutes and seconds and will calculate the total time in hours minutes and seconds e.g 2 hr, 15 min & 12 sec + 1 hr 10 min and 5 sec = 3 hrs 25 min and 17 sec

• how to access Qbasic
• menu system
• save and retrieve a program
• program development cycle
• software development cycle
• programming tools
• flowchart; pseudocode; top down charts

• If you wish for an intro to spreadsheets, please stay

• ADA: Named by Augusta Ada Byron, Countess of Lovelace, a mathematician in the 1800 who wrote the first computer program. ADA is based on Pascal and is supported to the US Department of Defence and requires its use on all US government military projects. The language is portable allowing transfer between computers.

• Pascal: Developed in Switzerland in 1968, named after Blaise Pascal who developed one of the earliest calculating machines. Developed for teaching programming and was one of the first programming languages where the instructions in the language were designed to encourage programmers to follow a structured program. New development ‘Turbo Pascal’ by Borland Corporation.

• Fortran: FORmular TRANslator developed by IBM in 1957. Designed to be used to scientists, engineers and mathematicians; considered to be the first high level language; noted for its capability to easily express and efficiently calculate mathematical equations.

• C: Developed in 1972 by Dennis Ritchie at Bell Laboratories; originally designed as a programming language for writing systems software but now general purpose language; very powerful; UNIX operating system is written in C.

• Cobol: COmmon Business Orientated Language. Key person in development was Admiral Grace Hopper in 1960. Development was backed by US Department of Defence. COBOL instructions are arranged in sentences and grouped into paragraphs; produces lengthy program code; very good for processing large files and simple business calculations.

• Basic: Beginner’s All-purpose Symbolic Instruction Code. Developed by John Kenneny and Thomas Kurtz in 1964. Designed to be simple interactive programming language for college students. Other versions include Microsoft Quickbasic, GWbasic, Qbasic etc

• Similar to c and c++
• developed for multimedia on Web
• creates small program called applets which are downloaded and run on your browser
• safe from virsus
• simple robust and portable
• object orientated
• developed by Sun MicroSystems
• JavaScript simplier version developed by Netscape

• Hyper Text Markup Language
• not strictly a programming language but does have specific syntax rules
• used for WWW - formating language to layout web pages with text graphics video and sound