Transcript Introduction to Qbasic

Introduction to Qbasic
Program Concepts
Readings
 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
This lecture
 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
•
•
•
•
•
•
•
•
•
•
•
•
•
•
1957 FORTRAN
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
Main Programming Languages
Basic
 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.
Write a program - comparison of
languages
 Program to compute gross amount due on
an invoice
 multiply unit price by quantity of the
purchase giving the gross amount
* compute net amount due
COBOL
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
/* 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};
C
C Compute gross amount due
gross = price *qty
C compute gross net amount due
IF (code = 0 ) then
net = gross
FORTRAN
ELSE
disc = .02 * gross
net = gross - disc
ENDIF
C Print net amount due
WRITE (CRTOUT.*) “The net amt due is $”,net
REM compute gross amt due
gross.amount = unit.price * quantity.purch
REM compute net amount due
IF discount.code = 0 THEN
net.amount.due = gross.amount
ELSE
discount = .02* gross.amount
net.amount.due = gross.amount - discount
ENDIF
REM print net amt due
PRINT USING “the net amt due
is$##,###.##”;net.amount.due
BASIC
COBOL
C

FORTRAN
BASIC
Accessing Qbasic
 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
Later Versions of Windows
 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
In the labs
 K Block
• start; programs; dos applications; quickbasic
 Z Block
• shortcut
Important keys
 ALT + enter to maximise screen
 Ctrl + break to stop a continuously looping
program
Qbasic Window
 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
Menus
 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
Program Development Cycle
 determine outputs - what is the question?
 determine inputs - what is the user
required to enter/ data available?
 determine process - algorithm /
mathematical formulas
Input
Process
Output
algorithm - step by step solution to the problem
Steps in Planning the program
 5 steps in the planning process
 ????
Program Planning
 Analysis - define the program
 Design - plan the solution; consider all
‘what if scenarios’
 Code - translate into (QBasic) language
 Test and Debug
 DOCUMENTATION!!!!!
Programming Tools
 Flowcharts
 Pseudocode
 Top-down charts
Flow charts
 represents the steps in
the algorithm in a
graphical manner
Start
payrate = 6.25
hours = 25
grosspay = payrate * hours
print grosspay
END
Your turn
 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”
Pseudocode
 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
Top - Down Chart
 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
A general solution?
Start
payrate = 6.25
hours = 25
grosspay = payrate * hours
print grosspay
END
Payrate = 6.25
hours = 25
grosspay = payrate * hours
PRINT grosspay
END
Variables
 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
Assignment of variables
x
X = 0.5
y = 10
z=x+y
total = z + x
y = total
x = 10
x = x+y
y
z
total
0.5
10
10.5
11
11
10
21
Variable names
 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...
Valid names
A
4sale
Test1
Rumplestiltskin
%Interest
Gross Pay
Grosspay
GroSSPay
Valid
invalid
valid
valid
invalid
invalid
valid
valid
Your turn
 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
Key points
 how to access Qbasic
 menu system
 save and retrieve a program
 program development cycle
 software development cycle
 programming tools
• flowchart; pseudocode; top down charts
 The End
 If you wish for an intro to spreadsheets,
please stay
ADA

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

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

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

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

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

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
Java
 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
HTML
 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