Learn QBasic =)
BASIC is a programming language that was introduced at Dartmouth college in 1964. The full form of BASIC is Beginner's All Purpose Symbolic Instruction Code.
After 21 years, later in 1985 Microsoft released their own version of BASIC called QBASIC with their MS-DOS operating system.
QBASIC is a high level language. Instructions (or commands) are written using english words that we use in our day to day life (Eg, PRINT, INPUT, FOR, NEXT ...). The instructions are interpreted and executable file is generated when we run a QBASIC program.
Files written in QBASIC have a .BAS extension.
We need an editor and an interpreter to be able to write and execute QBASIC programs into our computer.
QB64 is a program we are going to use for writing QBASIC program.
To download QB64 for Windows 10 in your computer from Github or QB64 website
A variable is a name which can contain a value.
A variable has a type which is defined by the kind of value it holds.
- String variable
- Numeric variable (integer, long, single, double)
If a variable holds symbols or texts, it is called a string variable (or character variable). If the variable holds a number, it is called long integer, single or double.
Integer and long can only store numbers. However, single and double can also store decimal values.
- STRING ➡ "Hello world"
- INTEGER ➡ 99
- LONG ➡ 98765
- SINGLE ➡ 99.2932
- DOUBLE ➡ 983288.18
Delcaring a variable is a way to tell the QBASIC program what type of value will be stored in a variable. We can declare variables using two ways.
- using DIM statements
The word DIM stands for DIMENSION. We use DIM statement to explicitly declare the variable as a type.
DIM name as string 'Laxmi Prasad Devkota
DIM height as integer '120
DIM price as single '199.99
-
appending symbols at the end of variable names QBASIC has a set of symbols to represent each variable type
-
$ String
-
% Integer
-
& Long
-
! Single
-
# Double
We can append these symbols at the end of variable names instead of using DIM statements to declare the type of the variable.
name$ 'Laxmi Prasad Devkota
height% '120
price! '199.99
Array is a variable which stores different values of the same data type. In array index starts at one.
Example:
DIM person(3) AS STRING
person(1) = "Prinsha"
person(2) = "Navadita"
person(3) = "Prabina"
FOR x = 1 TO 3
rand! = RND * 3
y% = INT(rand!)
IF y% >= 1 THEN
PRINT y%, person(y%),
END IF
NEXT x
Commands are instructions written in a program to do certain things. Often, they are also called as Statements. Since QBASIC is a high level language, those instructions are given using english language which we use in our day to day activities.
We use comments to add descriptions to a program or code blocks. It makes the code more readable. Comments never gets interpreted and executed.
There are two ways to put a comment in QBASIC.
They are:
- REM keyword (or REMARK)
- Single quote (')
Example:
'---------------------------------------
REM This program is all about Covid19
REM 01/01/2021
REM Written by : Covid19 (●'◡'●)
'---------------------------------------
We use Print keyword to display symbols, strings and numbers in the console (or Output).
There are two ways to print in QBASIC.
- ? (Question mark)
Example:
Print "Hi there"
Print "A quick brown fox jumps over the lazy dog"
? "Hello!" ` "Hello"
Sometimes we my require to clear the screen before we print something useful. We use CLS command to clear the screen.
You should be careful where to use this command as it will clear everything up from the screen from where it is used.
Example: The following program only prints I see you since Peek - a - Boo is cleared by CLS command
PRINT "Peek - a - Boo"
CLS ' clears everything before this line
PRINT "I see you"
Output : I see you
We can format output to meet our needs. We can use commas, semi-colons etc along with semi-colons PRINT statement to format output.
- Semi colon (;)
Using semi colon in between PRINT statements makes texts appear next to each other
PRINT "Hello";"World" ` "Hello World"
- Comma (,)
Using comma in between PRINT statements makes texts appear with spaces
PRINT "Hello","World" ` "Hello World"
- New line
We can use empty PRINT statement to print new line.
Example : The following program prints in separate lines since empty PRINT statement prints a new line
PRINT "Hello"
PRINT
PRINT "World"
Output :
Hello World
- Space or tab
We can use the SPACE$() or TAB() to add spaces while printing. The functions take integer parameter and prints the corresponding space in the output.
Example:
FOR I = 1 TO L STEP 1
PRINT SPACE$(I); I
NEXT I
Sometimes we need to ask for certain input from users before we perform some activities in our program. INPUT command is used to get input from the user.
When an INPUT is encountered, the system halts and waits for user input. We know this when there is a question mark and a blinking cursor in the Output
Example:
DIM grade as integer
Input "Enter your grade"; grade
Print "You entered"; grade
The process of repeating or printing a series of statements as many times as needed is called loop.
Example: The following program prints from 1 to 100 in sequence using FOR loop
FOR z = 1 TO 100
PRINT z;
NEXT z
SELECT CASE is used to determine the program flow by comparing the value of a variable to specific CASE values.
Example:
SELECT CASE num
CASE 1
PRINT 1;
PRINT " - one"
CASE 2
PRINT 2;
PRINT " - Two"
CASE 3
PRINT 3;
PRINT " - three"
CASE 4
PRINT 4;
PRINT " - four"
CASE 5
PRINT 5;
PRINT " - five"
END SELECT
It is used at the end of the QBASIC program to terminate it.
Syntax : End
The GOTO statement branches to a specific line number or to the specified label (or bookmark).
In the example below, the GOTO statement at the end branches the program to the beginning (after the "START" label).
Example:
START:
PRINT "Please enter a number from 1 to 3 ONLY"
PRINT
'INPUT "Please enter a number"; num%
rand! = RND * 3
num% = INT(rand!)
IF num% = 1 THEN
PRINT "It's number 1, Not badd"
ELSEIF num% = 2 THEN
PRINT "Ooo, Nice shot anyway ;)"
ELSEIF num% = 3 THEN
PRINT "It's number three"
ELSE
PRINT "This number is not available, sorryyy :/"
END IF
INPUT "Press enter key to continue"; n
CLS
GOTO START
RANDOMIZE TIMER initializes the random-number generator. RND returns a single-precision random number between 0 and 1.
The RND * 6 statement returns a random number that is greater than or equal to 0 and less than 6.
Example:
RANDOMIZE TIMER
FOR z = 1 TO 10
num = RND * 6
IF num >= 1 THEN
PRINT num; "="; INT(num)
END IF
NEXT z
Conditions are used in QBASIC to decide certain actions.
Conditional operators means to choose between two or more sections of the program to execute the program.
= , > , < , >= , <= are the examples of conditional operators.
The IF statement always asks a question (usually about the number in a variable.) If the answer is TRUE the true branch is executed. If the answer if FALSE the true branch goes to the ELSE statement. In both cases, the IF ELSE statement ends with the ENDIF statement.
Example:
INPUT "1 or 2? ", n%
IF n% = 1 OR 2 THEN
PRINT "Oh, ok"
ELSE
PRINT "Number not found"
END IF
LEFT$ returns specific number of characters from left side to supplied string and returns the value.
Example:
PRINT LEFT$("hello", 4) 'prints hell
PRINT LEFT$("welcome", 5) 'prints welco
RIGHT$ returns specific number of characters from right side to supplied string and returns the value.
Example:
PRINT RIGHT$("welcome", 4) 'prints come
The UCASE$ function converts all the strings to uppercase letters.
Example:
Test$ = "ITS just FoR testing"
PRINT Test$
PRINT UCASE$(Test$)
The LCASE$ function converts all the strings to lowercase letters.
Example:
Test$ = "ITS just FoR testing"
PRINT Test$
PRINT LCASE$(Test$)
ASC returns the ASCII code for the first character in a string expression.
Example:
PRINT ASC("Q") 'Output is: 81
PRINT ASC("Apple") 'Output is: 65
Example:
PRINT CHR$(81) 'Output is: Q
PRINT CHR$(97) 'Output is: a
...
...
- BASIC (Beginner's All Purpose Symbolic Instruction Code)
- ASCII (Americain Standard Code for Information Interchange)
1: http://pittajarn.lpru.ac.th/~nukit/basic/tutorial_basic.pdf
2: https://www QBASIC.net/en QBASIC-tutorials/beginner QBASIC-beginner-1.htm