QBasic and QBasic and Programming Programming PresentationPresentation

Prepared by:Obusan, Janssen Roselle T.

Opiana, Christian Joseph I.

QBasic

It all started back in 1963 when John Goerge Kemeny and Tom Kurtzas got together at Dartmouth College.

It is an interpreter which reads every line, translates it and lets the computer execute it.

NOTE: BASIC stands for Beginner’s All Purpose Instruction Code.

RulesRules and Its and Its FeatureFeature

QBasic programs are executed in the order

which they are written.

Every statement should have at least

one QBasic command.

All commands have to be written using the Syntax Rules.

Syntax is the grammar of writing.

It is a user friendly language.

It is widely known and accepted programming

language.

It is one of the most flexible

languages, as modification can easily be done.

Language is easy since the variables

can be named easily and uses simple English

phrases.

DataData(A collection of facts and figures that is entered into the computer.)(A collection of facts and figures that is entered into the computer.)

CONSTANTCONSTANT(Data whose values do not change)

Numeric Constant(numbers – negative or positive – used for mathematics)

e.g. 100

Alphanumeric Constant/String(numbers of alphabets written within double quoutes)

e.g. “computer”

VARIABLEVARIABLE(Data whose values can change fue to some calculation)

Numeric Variable(numbers that are constant for arithmetic)

e.g. A = 50

Alphanumeric Variable(variable that holds an Alphanumeric constant)

e.g. Name$ = “Akanksha”

Modes Modes (QBasic can be made to translate your instructions in two modes.)(QBasic can be made to translate your instructions in two modes.)

Direct Mode

Program Mode

Accepts single line instructions from the user and the output is viewed as soon as the key is pressed.

This mode is used to types a program which is stored in the memory. They have line numbers. We have to give the command to get the output.

Note: Every programming language has its own SYNTAX (rules) and COMMANDS.

Keywords and their FunctionsKeywords and their Functions

LISTUsed to list the

programs on the screen.

RUNUsed to execute

the program.

LLISTUsed to list the program as a

hardcopy.

LPRINTUsed to get the

output of the program on the hard copy.

NEWUsed to clear the

memory of a existing program.

Keywords and their FunctionsKeywords and their Functions

SYSTEMUsed to take

you back to dos prompt.

PRINT & CLSPrint is used to

display on screen.CLS is used to clear

the screen.

RMEUsed to show the

position of the mistake.

SAVEUsed to save the

program.

LOADUsed to load the program from the

disk to the memory.

QBasic CommandsQBasic CommandsCLS

This command is used to clear the screen.

PRINT

This command is used to display the output on the screen.

REM

It stands for ‘remark’. It makes the program more

understandable to the reader.

LET

It assigns a value to a variable in a program.

NOTE: A numeric data should be assigned to a numeric variable and aplhanumeric data to an alphanumeric variable.

QBasic CommandsQBasic Commands

END

This command is usually given at the end of the program.

INPUT

It allows the user to enter a value for the variable while running the program.

DELETE

To delete a line number in a program.

QBasic Reminders!QBasic Reminders!

A program consists of a line number.

It contains keywords like: PRINT, END etc.

Each program line begins with positive

number.

Run is used to execute a program.

It is possible to overwrite a statement but if you want to write a new program, use

the NEW command.

To exit the QBasic program, SYSTEM command is used.

NO TWO LINES

SHOULD HAVE SAME

NUMBER.

When the PRINT command, When the PRINT command, you can also print NUMBERS you can also print NUMBERS to the screen. Delete the to the screen. Delete the current program (unless you current program (unless you already have) and write the already have) and write the following:following:PRINT 512 (or ?512)PRINT 512 (or ?512)<press enter><press enter>Press F5 to run the program. Press F5 to run the program. The program outputs: The program outputs: 512512

COMMANDSCOMMANDS

There are also special There are also special functions called functions called “COMMANDS” (also “COMMANDS” (also called called “INSTRUCTIONS”). A “INSTRUCTIONS”). A “COMMAND” tells the “COMMAND” tells the QBASIC interpreter to do QBASIC interpreter to do something.something.The PRINT command The PRINT command tells the QBASIC tells the QBASIC interpreter to print interpreter to print something on the screen. something on the screen. In this case, the In this case, the interpreter printed interpreter printed “HELLO WORLD!”.“HELLO WORLD!”.

TIP: Instead of typing

PRINT, you can enter a

question mark. For

example:

?“HELLO WORLD!”

EXPRESSIONSEXPRESSIONS

An expression is something the interpreter An expression is something the interpreter calculates (or evaluates). Such as:calculates (or evaluates). Such as:

1+11+1 (returns 2)(returns 2)100-147100-147 (returns 53)(returns 53)3*343*34 (returns102)(returns102)80/480/4 (returns 20)(returns 20)(100*3)+56(100*3)+56 (returns 356)(returns 356)

I f you pass an expression to the PRINT command, the value returned

(a number) is printed.

Clear the current program and then run the following:

PRINT 512+478

PROGRAM OUTPUT:990

if you enclose the expression with quotation marks, the expression becomes a str ing and isn’t evaluated. For example:

PRINT “512+478OUTPUT512+478

ACTIVITYACTIVITY

1.1. EVALUATE:EVALUATE:A.A. 14/2-3*1=14/2-3*1=B.B. 8*2/(5-1)=8*2/(5-1)=C.C. 3+5^2*4=3+5^2*4=D.D. 4+(3*2-1)^2/5=4+(3*2-1)^2/5=

ACTIVITY(Continuation)ACTIVITY(Continuation)

2. EXPRESS IN INTEGER OR DECIMAL 2. EXPRESS IN INTEGER OR DECIMAL FORMFORMA.A.5.0D+7=5.0D+7=B.B.-1.23D+03=-1.23D+03=C.C.1.234D-04=1.234D-04=D.D.4.26305D+084.26305D+08

RETRIEVING KEYBOARD RETRIEVING KEYBOARD INPUT FROM THE USERINPUT FROM THE USER

One way to receive input from the keyboard is with the INPUT command. The INPUT command allows the user to enter either a string or a number, which is then stored in a variable.INPUT data$PRINT data $

When is the program executed, the INPUT command displays a question

mark, followed by a blinking cursor. And when you enter text, the program stores that text into the variable data$, which is

printed to the screen.

TIP: if you place a string and a semi-colon between INPUT and the variable, the program will print the string.INPUT “ENTER SOME TEXT:”; data$

To receive a number, use a To receive a number, use a non-string variable.non-string variable.INPUT numberINPUT numberPRINT numberPRINT numberIf you enter text instead of a If you enter text instead of a number, the QBASIC number, the QBASIC interpreter displays an error interpreter displays an error message (“Redo from message (“Redo from start”).start”).

RETRIEVING KEYBOARD RETRIEVING KEYBOARD INPUT FROM THE USERINPUT FROM THE USER

Below is another example of the INPUT command:

PRINT “Enter some text:”INPUT text$

PRINT “Now enter a number:”

INPUT numPRINT text$PRINT num

THE IF AND THEN COMMANDS

The IF and THEN commands are used to compare an expression and then perform some task based on that expression.X=5IF X=5 THEN PRINT “ X equals 5”Since X does equal 5 in this case, the program outputs:

X equals 5

EXPRESSION SIGNSYou can also enter the following statements, instead of the equals sign:X<5 (x is less than 5)X>5 (x is greater than 5)Run the following: X=16IF(X>5) THEN PRINT “X is greater than 5”

THE IF AND THEN COMMANDSTHE IF AND THEN COMMANDS

You can also combine the signs l ike this:

x<=5 (x is less than or equal to 5)

X>=5 (x is greater than or equal to 5)

X<>5 (x does not equal to 5)

Run the following example:CLSX=5

IF (X>=5) THEN PRINT “X is greater than equal to 5”

IF (X<=5) THEN PRINT “X is less than or equal to 5”

IF (X<>5) THEN PRINT “X does not equal to 5”

OUTPUT:X is greater than or equal to

5X is less than or equal to 5

ELSEELSE Using the ELSE command, you can

have the program perform a dif ferent action if the statement is false.

x=3IF x=5 THEN PRINT “Yes” ELSE PRINT

“No”Since X doesn’t equal to 5, the output

is:No

END IFEND IF al lows you to have mult iple

commands after the IF… THEN statement, but they must start on

the l ine after the IF statement. END IF should appear r ight after the l ist

of commands.

Prepared by:Prepared by:Obusan, Janssen Roselle T.Obusan, Janssen Roselle T.Opiana, Christian Joseph I.Opiana, Christian Joseph I.