Introduction to Programming and QBasic Tutorial

INTRODUCTION to
Programming and QBasic
By: Nyrhon Von V. Bautista
and Mhon Vincent S. Saldivar
JGMNHS G9-SSC-Lavoisier

Programming???? A brief background
• Programming is a set of step by step instructions
that tells or direct the computer what to do. It
sequences the tasks a user wants to be done and
produces the results or output needed.
• The set of rules or instructions that tells the
computer what to perform is done through a
programming languange. In this tutorial we will
use the QBASIC programming language.
• A programmer is the person who designs a
program.

Planning the
Solution
Coding the
Program
Testing the
Program
-Desk Checking
-Translation
-Debugging
Documentation
Identifying the
Problem
PROGRAM
LIFE
CYCLE

Did you know that the first
programmed word is
“HELLO WORLD”
LEVELS OF PROGRAMMING LANGUAGES
Machine Language or First Generation Programming Language
-this is considered to be the lowest level of programming
language.
Assembly Language or Second Generation of Programming
Language
-instead of using 1s and 0s assembly language uses MNEMONIC
Codes. Mnemonic codes are abbreviations that easy to
remember
High Level Language or Third Generation Programming
Language
-this language transformed programming in the early 1960’s.
Very High Level Languages or Fourth Generation Languages
-Fourth generation languages (4GL) simplifies further the third
level generation languages.
Natural Languages
- These languages are considered to be the fifth
Generation languages. These programming languages are called
Natural Languages because of their resemblance to
English Language.

Procedural Languages
Programming languages which are considered
procedural that uses a series of instructions or statements which
are sequential from the beginning to the end.
Examples of Procedural Languages:
BASIC – Beginner’s All-Purpose Symbolic Instruction Code
COBOL – Common Business Oriented Language
PASCAL
FORTRAN- Formula Translator
C
PL1 – Programming Language One

Non-procedural
Languages
These Programming languages are considered as object-
oriented programming languages. It is different from
procedural language since statements are not executed line
per line instead a series of instructions are executed as a whole
when an event occurs.
Examples of Non-procedural Languages
VISUAL BASIC
C++
JAVA
DELPHI

FLOWCHARTING
Flowcharting is one of the processes used in
designing or planning the solution to a
problem. It is a graphical representation to the
solution of a problem. It uses shapes to show
instructions and arrow lines and heads to
display the flow. It uses the shapes OVAL,
PARALLELOGRAM, RECTANGLE,
DIAMOND,CIRCLE & PENTAGON

Oval Terminal Symbol
Parallelogram Input/Output
Rectangle Process
Diamond Decision
Hexagon Initialization/Preparation
Arrow Lines & Arrow
Heads
Direction
Annotation
Circle On Page Connector
Pentagon Odd-Page connector

Qbasic Tutorial
After launching the QBasic interpreter (see before you start), you might
see a window requesting a list of "parameters." If this window comes up,
press the Enter key to continue.
You should now see the QBasic interpreter, which has a blue
background and displays a dialog box at the center. (If the interpreter
fills the entire screen, then you may want to press "Alt + Enter," to make
it smaller.)
Press the Esc key to hide the dialog box.
QBasic interpreter - main screen

Type the following (including the quotation marks) in the QBasic interpreter:
PRINT "Hello World!" <press Enter>
Now press F5 to run the program. You should now see a black screen,
with Hello World at the top, and Press any key to continue at the bottom.
Press a key on the keyboard to return to the main screen.
(The figure below displays the "output screen.")
Basic interpreter - output screen
If you run the program again, the interpreter adds another Hello World. QBasic
adds Hello World each time the program is run.

Deleting the program
To erase the current program:Go to the "File" menu.
Click "New."
The interpreter asks if you want to save the program.
Select "No" (or if you'd rather keep the program, select "Yes").
Strings
There are certain types of data (or information) called "strings." Strings contain a sequence of
characters (letters, numbers, and symbols) enclosed in quotation marks. For
example, "Hello World!" is a string.
The following are also strings:
"0123456789"
"This is a string"
"abc123"
"1 + 1 = 2"

Commands
There are also special functions called "commands" (also called "instructions").
A "command" tells the QBasic interpreter to do something.
The PRINT command tells the QBasic interpreter to print something to the
screen. In this case, the interpreter printed"Hello World!".
TIP: Instead of typing PRINT, you can enter a question mark. For example:
?"Hello World!"
With the PRINT command, you can also print numbers to the screen. Delete
the current program (unless you already have) and write the
following:PRINT 512 (or ?512)
<press Enter>
Press F5 to run the program. The program outputs:512

More about the PRINT command
You can use multiple print statements in your program.PRINT "Hello"
PRINT "World"
Output:Hello
World
To place World onto the previous line, place a semi-colon
after PRINT "Hello".PRINT "Hello";
PRINT "World"
Output:HelloWorld
Also, if you put a comma instead of a semi-colon on the first line, the program will
insert spaces between the two words.PRINT "Hello",
PRINT "World"
Output:Hello World

Variables
This chapter discusses an important topic in programming, "variables." Please read
this section thoroughly.
A variable is a piece of data kept in the computer's memory (RAM). The location of a
variable in RAM is called the"address."
How a variable is stored in RAM
The following program prints the variable X to the screen:print X
Since the variable hasn't been assigned a number, the value of the variable is 0. So, the
output of the program is:0
This next program sets X to 15, and then prints the variable:
X = 15
print X
This time, the output is:15
In the above example, the number 15 was stored in the computer's RAM at a certain
memory address. Then the PRINTcommand accessed (or looked at) that address when it
printed "15" to the screen.

Expressions
If you pass an expression to a variable, the expression is evaluated and the variable is set to that
value.x = 500 + (10 * 7)
PRINT x
Output:570
You can also use variables as expressions.rate = 50
time = 2
distance = rate * time
PRINT distance
Output:100
Plus, you can have both variables and numbers in an expression.X = 100
Y = X * 7
PRINT Y
Output:700
TIP: The following increases X by 1:
X = X + 1

Strings
If you add a dollar sign ($) to the end of a variable, the variable is a string.X$ = "Hello World!"
PRINT X$
Output:Hello World!
If you try to set a string to a non-string variable, an error occurs.X = "Hello World!"
The QBasic interpreter says "Type mismatch" when you try to run the above program.
A string can be added to the end of an existing variable string.X$ = "Hello"
X$ = X$ + "World"
PRINT X$
Output:HelloWorld
You can also add variable strings together.a$ = "String1"
b$ = "String2"
c$ = "String3"
d$ = a$ + b$ + c$
PRINT d$
Output:String1String2String3

Retrieving keyboard input 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 this program is 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 non-string variable.INPUT number
PRINT number
If you enter text instead of a number, the QBasic interpreter displays an error
message ("Redo from start").

To receive a number, use a non-string variable.INPUT number
PRINT number
If you enter text instead of a number, the QBasic interpreter displays an error
message ("Redo from start").
Below is another example of the INPUT command:PRINT "Enter some text:"
INPUT text$
PRINT "Now enter a number:"
INPUT num
PRINT text$
PRINT num
TIP: You can have the question mark displayed on the previous line by using a
semi-colon.
PRINT "Enter some text:";
INPUT text$

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 = 5
IF x = 5 THEN PRINT "x equals 5"
Since X does equal 5 in this case, the program outputs:x equals 5
Expression signs
You 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 = 16
IF (x > 5) THEN PRINT "x is greater than 5"
Output:x is greater than 5

ELSE
Using the ELSE command, you can have the program perform
a different action if the statement is false.x = 3
IF x = 5 THEN PRINT "Yes" ELSE PRINT "No"
Since X doesn't equal 5, the output is:No
END IF
END IF allows you to have multiple commands after the IF...THEN statement,
but they must start on the line after theIF statement. END IF should appear
right after the list of commands.x = 5
IF (x = 5) THEN
INPUT a$
PRINT a$

END IF
The following program uses ELSE with the END IF command:x = 16
IF (x = 5) THEN
INPUT a$
PRINT a$
ELSE
PRINT x * 2
END IF
Output:32
TIP: There is a way to have multiple commands after IF...THENwithout
using END IF. To do so, place a colon between each command.
IF (x = 5) THEN INPUT a$: PRINT a$

THANK
YOU
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Introduction to Programming and QBasic Tutorial

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Introduction to Programming and QBasic Tutorial