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Beginner's Programming Tutorial in QBasic
This document is meant to get you started into programming, and assumes you have some experience with computers and with Windows 95 (or 98, etc.). Since this tutorial is written for people who don't like to read a lot of text, it includes a number of examples. Therefore, you can do a lot of work in not much time. The more important chapters have a star ( ).
Feel free to distribute this tutorial, upload it to your website, link to it from your site, etc. http://www.geocities.com/progsharehouse/qbtutor Mirror: http://development.freeservers.com/qbtutor

Table of Contents
Part I: Q-Basics
Chapter 1: Before you start Chapter 2: Your first program Chapter 3: Variables Chapter 4: Retrieving keyboard input from the user Chapter 5: The IF and THEN commands Chapter 6: Labels and the GOTO and GOSUB commands Chapter 7: Loops Chapter 8: What next?

Part II: Intermediate topics
Chapter 9: QBasic interface Chapter 10: Adding documentation to your programs Chapter 11: Reading and writing to files Chapter 12: Displaying graphics Chapter 13: Mathematics functions Chapter 14: Getting the current date and time

Part III: Advanced topics
Chapter 15: Arrays Chapter 16: Variable types Chapter 17: Subroutines and functions Chapter 18: Numbering systems Chapter 19: Memory

Before you start
Before you can create a program in QBasic, you need the QBasic interpreter. It is available from your Windows 95 (or 98) CD, or you can download it below. To access QBasic from the Windows 95 CD:
1. Insert the CD into your CD-ROM drive. 2. Click "browse this CD" (if the menu screen doesn't come up, then browse the CD from My Computer. 3. Go to the \OTHER\OLDMSDOS directory. 4. Open a program called QBASIC.EXE (this is version 1.1 of the QBasic interpreter).

To access QBasic from the Windows 98 CD:
1. Insert the CD into your CD-ROM drive. 2. Click "browse this CD" (if the menu screen doesn't come up, then browse the CD from My Computer. 3. Go to the \TOOLS\OLDMSDOS directory. 4. Open a program called QBASIC.EXE (this is version 1.1 of the QBasic interpreter).

Download it here (right-click and press "Save As"):
QBASIC.ZIP (323 KB) - QBasic 1.1 interpreter and sample programs UNZIP32.EXE (90 KB) - Extracts the ZIP file

To unzip the QBASIC.ZIP file with UNZIP32.EXE:
a. Go to the Start Menu b. Click Run... c. Type the following (this loads MS-DOS): command

d. Enter the following in DOS (assuming you saved QBASIC.ZIP to C:\QBASIC): cd c:\qbasic unzip32 -n qbasic.zip

Your first program
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!"

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.")

QBasic 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: 1. Go to the "File" menu. 2. Click "New." 3. The interpreter asks if you want to save the program. 4. 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 F5 to run the program. The program outputs: 512

Expressions
An expression is something the interpreter calculates (or evaluates). Such as: 1 + 1 100 - 47 3 * 34 80 / 4 (100 * 3) + 56 (returns 2) (returns 53) (returns 102) (returns 20) (returns 356)

NOTE: The asterisk (*) means to multiply two numbers; the slash (/) means to divide

If 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 string and isn't evaluated. For example: PRINT "512 + 478" Output: 512 + 478

TIP: To clear the output screen, use the CLS command. CLS

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 PRINT command accessed (or looked at) that address when it printed "15" to the screen.

(NOTE: The memory address of X is not necessarily 1000000)

ADVANCED TIP: Although you don't normally need to, you can find the actual memory address of a variable (X, for example) by using the VARSEG and VARPTR commands. PRINT (VARSEG(X) * 65536) + VARPTR(X) (For more information, see Memory.)

As in the programs above, a variable is accessed by calling its name. Variable names can have a combination of letters and numbers. The following are valid variables: Y num VALUE xYz abc123

Also, you can use multiple variables in your program. X = 82 Y = 101 Z = 79 PRINT X PRINT Y PRINT Z Output: 82 101 79

(NOTE: The memory addresses of these variables are not necessarily as specified)

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"). 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 You can also combine the signs like 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 5) Run the following example: CLS x = 5 IF (x >= 5) THEN PRINT "x is greater than or 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 5"

Output: x is greater than or equal to 5 x is less than or equal to 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 the IF 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...THEN without using END IF. To do so, place a colon between each command. IF (x = 5) THEN INPUT a$: PRINT a$

ELSEIF
The ELSEIF command allows you to perform a secondary action if the first expression was false. Unlike ELSE, this task is only performed if a specified statement is true. x = 6 IF (x = 5) THEN PRINT "Statement 1 is true" ELSEIF (x = 6) THEN PRINT "Statement 2 is true" END IF Output: Statement 2 is true

You can have multiple ELSEIF commands, along with ELSE. x = 8 IF (x = 5) THEN PRINT "Statement 1 is true" ELSEIF (x = 6) THEN PRINT "Statement 2 is true" ELSEIF (x = 7) THEN PRINT "Statement 3 is true" ELSE PRINT "No above statements are true" END IF Output: No above statements are true

Multiple expressions
You can have more than one expression in IF...THEN by using either the OR operator or the AND operator. The OR operator only requires one expression to be true in order to print "Yes" in the following program: x = 20 IF (x = 5 OR x = 20) THEN PRINT "Yes" Output: Yes

The AND operator requires both expressions to be true. x = 7 IF (x > 5 AND x < 10) THEN PRINT "True" Output: True This is a slightly more complex example: x = 16 y = 3 IF ((x > 5 AND x < 10) OR y = 3) THEN PRINT "Correct" Output (since Y is 3): Correct

Strings in IF...THEN
So far in this chapter, we've only been dealing with numbers, but you can also use strings with the IF...THEN command. x$ = "Hello" IF (x$ = "Hello" OR x$ = "World") THEN PRINT x$ Output: Hello

You can also compare two variable strings: x$ = "Hello" y$ = "World" IF (x$ <> y$) THEN PRINT x$; " "; y$ Output: Hello World

Labels and the GOTO and GOSUB commands
The GOTO and GOSUB commands enables you to jump to certain positions in your program. Labels are used to specify what point in the program to continue execution.

GOTO
To use GOTO, place a label somewhere in your program, and then enter. GOTO Run the following example program: PRINT "1" GOTO TheLabel PRINT "2"

TheLabel: PRINT "3" Output (notice how PRINT "2" is skipped): 1 3

TIP: TheLabel can be placed on the same line as PRINT "3" TheLabel: PRINT "3"

GOSUB
The GOSUB command is the same as GOTO, except when it encounters a RETURN statement, the program "returns" back to the GOSUB command. In other words, RETURN continues program execution immediately after the previous GOSUB statement. PRINT "1" GOSUB TheLabel PRINT "2" END

TheLabel: PRINT "3" RETURN (Note: The END command exits the program.) Since the program returns to the GOSUB command, the number 2 is printed this time. 1 3 2

Line numbers
"Line numbers" can be used as labels. PRINT "1" GOTO 10 PRINT "2" 10 PRINT "3" (Notice the line number)

You can also write the program like this: 10 PRINT "1" 20 GOTO 40 30 PRINT "2" 40 PRINT "3" The line numbers don't even have to be in sequence. 17 PRINT "1" 2 GOTO 160 701 PRINT "2" 160 PRINT "3" Each of these programs output: 1 3

Guessing game
The following is a simple guessing game: CLS start: PRINT "Guess a number between 1 and 10: "; INPUT num IF (num < 1 OR num > 10) THEN PRINT "That is not between 1 and 10" GOTO start END IF IF (num = 6) THEN PRINT "Correct!!!" ELSE PRINT "Try again" PRINT GOTO start END IF Output (may be slightly different): Guess a number between 1 and 10: ? 2 Try again Guess a number between 1 and 10: ? 7 Try again Guess a number between 1 and 10: ? 6 Correct!!!

TIP: Notice the second PRINT statement under PRINT "Try again". It adds a blank line under Try again when the program is executed.

Loops
"Loops" make it easier to do an action multiple times. There are at least four types of loops: IF...GOTO, WHILE...WEND, DO...LOOP, and FOR...NEXT.

IF...GOTO
This program uses IF...GOTO to create a loop: x = 10 start: PRINT x x = x + 1 (This adds 1 to x)

IF x < 15 THEN GOTO start Output: 10 11 12 13 14

WHILE...WEND
The WHILE...WEND commands continue a loop until a specified expression is false. To use WHILE...WEND: 1. Place an expression after WHILE 2. Enter a list of commands 3. Place WEND at the end Run the following: x = 10 WHILE x < 15 PRINT x x = x + 1 WEND

Output (same as in previous example): 10 11 12 13 14

DO...LOOP
DO...LOOP is exactly the same as WHILE...WEND, except it has at least two slight advantages. With DO...LOOP you can: 1. Loop until an expression is true 2. Loop at least one time regardless of whether the expression is true or not. To use DO...LOOP: 1. Specify whether the loop continues "while" the expression is true or "until" the expression is true, using the WHILE and UNTIL statements, respectively. 2. Place an expression after WHILE/UNTIL 3. Enter a list of commands 4. Place LOOP at the end The following uses the WHILE statement: x = 10 DO WHILE x < 15 PRINT x x = x + 1 LOOP

This program uses the UNTIL statement: x = 10 DO UNTIL x = 15 PRINT x x = x + 1

LOOP They both output: 10 11 12 13 14 If you place the expression at the end of the loop instead, the program goes through the loop at least once. x = 32 DO PRINT x x = x + 1 LOOP WHILE x < 5 This is the output because the loop was only gone through one time: 32

FOR...NEXT
FOR...NEXT provides an easier way to create a loop. FOR x = 1 TO 5 PRINT x NEXT x Output: 1 2 3 4 5

TIP: The X after NEXT is optional (unless you have a loop within a loop).

Also, you can use the STEP attribute to specify how much X will be increased each time through the loop. FOR x = 1 TO 5 STEP 2 PRINT x NEXT x Output: 1 3 5

STOPPING LOOPS
To stop a loop prematurely, use the EXIT command, followed by either FOR or DO. FOR x = 1 TO 5 PRINT x IF (x = 3) THEN EXIT FOR NEXT x Output: 1 2 3 (NOTE: This command only works with the DO...LOOP and FOR...NEXT commands, not with WHILE...WEND or IF...GOTO.)

What next?
Congratulations! You've finished part 1 of this tutorial. The remaining chapters cover additional topics, and don't have to be read in sequence (one after another). If you want, you can move on to a more advanced programming language. The rest of this chapter briefly explains how you can start using the most popular ones. One reason you may want to move on, at least at some point, is because QBasic has minimal capabilities. One example of this is that you can't create executable programs (EXE files) in QBasic. (QuickBasic 4.5 can create these files, but this product is no longer on the market.)

Other programming languages
Information about the below programming languages can be found at ProgrammingTutorials.com. C and C++ You can learn C by going to www.cm.cf.ac.uk/Dave/C/CE.html, www.strath.ac.uk/CC/Courses/NewCcourse/ccourse.html, or www.programmingtutorials.com/tutorial.asp?id=C. Before you can create an EXE file in C, you must have a compiler. I recommend downloading the DJGPP compiler (www.djgpp.com). This program is free, however, the author does accept donations. See below for information on getting DJGPP. You may also want to get the Allegro programming library. This library is useful for creating games in C. (NOTE: C++ is a more powerful version of C. It introduces "object oriented" programming. I recommend learning C++ before moving on to Visual C++.) Visual C++ With Visual C++, you can create Windows 95 programs, instead of DOS. It costs about $100 for the standard version. For more information, click here. To purchase Visual C++, click here. Visual Basic Visual Basic is similar to QBasic. So, if you are highly involved in QBasic, then you may want to switch directly to Visual Basic, instead of learning C/C++ or Visual C++.

With Visual Basic, like Visual C++, you can create Windows 95 programs. It costs about $100 for the "learning" edition. For more information, click here. To purchase Visual Basic, click here.

Getting DJGPP
Since the installation instructions for DJGPP are a little confusing, I've provided my own below. For more information about DJGPP, visit the DJGPP website at www.delorie.com/djgpp.

Installing DJGPP
1. Create a new folder called DJGPP in drive C. 2. Download and save each of the following to the DJGPP folder: (If any of the links below are out of date, or if you want to download more DJGPP packages, you can find the most current files here.) bnu211b.zip (2.6 MB) - Basic assembler, linker djdev203.zip (1.5 MB) - DJGPP Basic Development Kit faq230b.zip (0.6 MB) - Frequently Asked Questions gcc2953b.zip (1.9 MB) - GCC compiler gpp2953b.zip (1.7 MB) - C++ compiler mak3791b.zip (0.3 MB) - Make (processes makefiles) rh1478b.zip (2.0 MB) - RHIDE, an Integrated Development Environment, has a built-in editor and debugger txi40b.zip (0.6 MB) - Info file viewer unzip32.exe (0.1 MB) - Extracts the ZIP files 3. Unzip each of the files to the DJGPP folder. If you are using UNZIP32.EXE: a. Go to the Start Menu

b. Click Run... c. Type the following (this loads MS-DOS): command

d. Enter the following in DOS: cd c:\djgpp unzip32 -n *.zip 4. Edit your AUTOEXEC.BAT file. a. Go to the Start Menu b. Click Run... c. Type the following (you can "copy and paste" it): notepad c:\autoexec.bat d. Add the following lines to the end of the file (you can "copy and paste" this also): set DJGPP=C:\DJGPP\DJGPP.ENV set PATH=C:\DJGPP\BIN;%PATH% e. Go to the File menu. f. Click Save.

g. Close the program. 5. Restart your computer. 6. Run a program called RHIDE.EXE in the c:\djgpp\bin folder.

QBasic interface
This chapter gives a brief overview of the QBasic interface. The interface has the following features: 1. Window displaying the current program 2. Menu 3. Name of current program 4. Window to immediately execute a command 5. Status bar 6. Status of Caps Lock and Num Lock 7. Current line of cursor 8. Current column of cursor

QBasic interface

Current program
The current program is displayed in the middle of the screen, and covers most of the QBasic interface.

Menu
The menu provides most of the operations for the QBasic editor. Such as opening a file, pasting text, and searching for a string.

File

New - Clears the current program Open - Loads a program from disk Save - Saves the current program to disk Save As - Saves the program, but under a different name Print - Prints the selected text, current window, or entire program Exit - Closes the QBasic interpreter

Edit

Cut - Removes the selected text and stores it in the clipboard Copy - Copies the text instead of removing it Paste - Adds the text in the clipboard to the current position of the cursor Clear - Removes the text without storing it to the clipboard New Sub - Enables you to create a new subroutine (see Subroutines and Functions) New Function - Enables you to create a new function (see Subroutines and Functions)

View

SUBs - Shows the list of current subroutines and functions (see Subroutines and Functions) Split - Displays the contents of the current program in two windows. If the window is already split, this hides the second window (NOTE: The text in each window is always the same, even if you alter the text in one window) Output Screen - Shows the QBasic output screen.

Search

Find - Allows you to search for a string of text in the program Repeat Last Find - Continues the previous search operation Change - Replaces each instance of a string with another string

Run

Start - Executes the current program Restart - Starts from the beginning Continue - Continues execution at the current position

Debug

Step - Processes the next command Procedure Step - Processes the next command, but does not show QBasic going inside a subroutine or function Trace On - Shows the command that is being executed while the program is running Toggle Breakpoint - Sets or removes a breakpoint. Use this to have the QBasic interpreter stop when it reaches a specified line in the program Clear All Breakpoints - Removes all breakpoints in the program Set Next Statement - Allows you to continue execution at the specified line

Options

Display - Enables you to change display colors, the number of spaces to use for tabs, and whether or not scroll bars are visible Help Path - The location of the QBASIC.HLP file Syntax Checking - Allows you to have the QBasic editor check the syntax of your program as you type

Help

Index - List of all QBasic commands, keywords, operators, etc. Contents - The table of contents for QBasic help Topic - Show help for a specific keyword Using Help - Displays information on using QBasic help About - Shows information about the QBasic interpreter

Name of current program
The file name of the current program is displayed near the top of the screen in the center. You can change the name by selecting "Save As" on the "File" menu.

Immediately execute a command
QBasic provides a way to execute a command without running the current program. To do so, select the bottom window (under "immediate") and enter a command, then press Enter.

Status bar
The status bar is at the bottom of the screen. It displays a short list commands ( ). When you highlight an item on the menu, the status bar displays a short description of what the item does.

Status of Caps Lock and Num Lock
If Caps Lock is set, a "C" is displayed on the right side of the status bar. If Num Lock is set, an "N" is displayed on the right side of the status bar.

Current line
On the right side of the status bar, the current line of the cursor is displayed.

Current column
On the right side of the status bar, the current column of the cursor is displayed (immediately after the current line).

Adding documentation to your programs
Documenting your program (also called "commenting") allows you to remind yourself about something in your program. Plus, if your program is seen by other people, documenting can help them understand your code. The REM (remark) command enables you to add comments to your program without the text being treated like an instruction. CLS PRINT "Some text" REM This text is ignored. REM This program clears the output screen, REM and then prints "Some text."

TIP: You can use an apostrophe instead of the REM command. ' Comment goes here

You can add REM to the same line as another command by placing a colon after the first instruction. CLS: REM This command clears the screen PRINT "Text": REM This command prints "Text" to the screen PRINT 534: REM This prints the number 534 to the screen NOTE: If you use an apostrophe instead of REM while doing this, you do not need to add a colon. CLS PRINT "Text" PRINT 534 ' This command clears the screen ' This command prints "Text" to the screen ' This prints the number 534 to the screen

Reading and writing to files
To save data to a file: 1. Call the OPEN command, specifying the file name, file mode (OUTPUT), and file number. 2. Use PRINT, followed by the file number and the data you want to write. 3. Close the file using the CLOSE command. The following opens a file, using mode OUTPUT and number 1, and then saves the text Hello World! to the file: OPEN "testfile.dat" FOR OUTPUT AS #1 PRINT #1, "Hello World!" CLOSE #1

To open a file for "reading," call OPEN and pass INPUT as the file mode. Then you can read the data by using the INPUT command. OPEN "testfile.dat" FOR INPUT AS #1 INPUT #1, text$ CLOSE #1 PRINT text$ Output: Hello World!

Displaying graphics
Before you can show graphics images on the screen, you must call the SCREEN command. SCREEN sets the graphics mode. The following program uses graphics mode 13 (320x200) to display a line, then returns back to text mode: SCREEN 13 ' This starts at 10 pixels from the left, 10 from ' the top and goes to point (100, 100): LINE (10, 10)-(100, 100) WHILE INKEY$ = "": WEND SCREEN 0 ' Waits until a key is pressed

' Returns to text mode

You can also draw a colored line. SCREEN 13 LINE (10, 10)-(100, 100), 192 WHILE INKEY$ = "": WEND SCREEN 0 ' Dark green

To draw a single pixel, use PSET. SCREEN 13 PSET (160, 100) WHILE INKEY$ = "": WEND SCREEN 0 The following displays a circle at (160, 100) with a radius of 50: SCREEN 13 CIRCLE (160, 100), 50 WHILE INKEY$ = "": WEND SCREEN 0

Finally, to display a square, use LINE. SCREEN 13 LINE (10, 10)-(100, 100), 192, B WHILE INKEY$ = "": WEND SCREEN 0 ' Notice the B

Mathematics functions
QBasic provides several functions to do mathematical calculations. A few of them are discussed here.

SQR
Use SQR to find the "square root" of a number. PRINT PRINT PRINT PRINT PRINT Output: 1 2 3 4 5 SQR(1) SQR(4) SQR(9) SQR(16) SQR(25)

ABS
ABS returns the absolute value of a number. In other words, ABS converts a negative number to a positive number (if you pass a positive number, ABS does nothing). PRINT ABS(12) PRINT ABS(-12) Output: 12 12

COS, SIN, TAN, and ATN
You can do the following trigonometric functions in QBasic: COS SIN TAN ATN (Cosine) (Sine) (Tangent) (Arctangent, inverse of TAN)

Example: CONST PI = 3.141593 PRINT PRINT PRINT PRINT Output: .7071067 .8660254 6137956 1.570796 COS(PI / 4) SIN(PI / 3) TAN(-PI / 2) ATN(TAN(-PI / 2))

(Same as PI / 2)

Getting the current date and time
To get the current time, use the TIME$ command. PRINT TIME$ The above example returns "military" time. See the following figure: hour 00 = 12 a.m. (midnight) hours 01-11 = a.m. hours 12-23 = p.m.

You can also use TIME$ to set the time. TIME$ = "15:30:00" ' Sets current time to 3:30 p.m.

Date
To find out the current date, use the DATE$ function. PRINT DATE$ Like TIME$, you can also set the date. DATE$ = "01/01/2000"

TIMER
Use TIMER to get the number of seconds since midnight. PRINT TIMER Output: 43199.99 (Just before noon)

Arrays
An array is a list of variables of the same type. Arrays are useful for organizing multiple variables. To create an array, use the DIM (dimension) command. The following example does not use arrays: a b c d e = = = = = 2 4 6 8 10

PRINT a, b, c, d, e Output: 2 4 6 8 10

This uses an array called vars, which contains 5 variables: DIM vars(5) ' Each of vars(1) = vars(2) = vars(3) = vars(4) = vars(5) = these are separate variables: 2 4 6 8 10

PRINT vars(1), vars(2), vars(3), vars(4), vars(5) Output: 2 4 6 8 10

How an array of variables is stored in memory (NOTE: Memory addresses are not necessarily as specified)

The above program can also be written like this: DIM vars(5) FOR x = 1 to 5 vars(x) = x * 2 NEXT FOR x = 1 to 5 PRINT vars(x), NEXT Output: 2 4 6 8 10

Strings
You can also create an array of string variables. DIM vars$(5) vars$(1) vars$(2) vars$(3) vars$(4) vars$(5) = = = = = "Two" "Four" "Six" "Eight" "Ten"

PRINT vars$(1), vars$(2), vars$(3), vars$(4), vars$(5) Output: Two Four Six Eight Ten

Variable types
The non-string variables we've used in this tutorial are actually called single-precision variables. These types of variables (SINGLE's) are used to store numbers that can contain a decimal value (such as 1.89 or 3.141593). Since they have decimal values, they are also known as "floatingpoint" variables. This chapter describes other types of variables used in QBasic. INTEGER - A non-floating-point variable (no decimal value) that can store integers between -32,768 and 32,767 LONG - Same as INTEGER, but can contain numbers between -2,147,483,648 and 2,147,483,647. DOUBLE - Same as SINGLE, but can have twice as many digits. To define a variable's type, use DIM with the AS attribute. DIM var1 AS INTEGER DIM var2 AS LONG DIM var3 AS DOUBLE var1 = 15.28 var2 = -2000000000 var3 = 12345678.12345678 PRINT var1 PRINT var2 PRINT var3 Output: 15 (Notice how the decimal value is removed) -2000000000 12345678.12345678

Using special characters
You can use special characters to specify a variable's type. These characters can also be used to specify a number's type. To do so, place one of the following at the end of a variable (or number): ! % & # (single--actually, this doesn't change anything) (integer) (long) (double)

$

(string--as we already know)

Example (notice the number sign on 12345678.12345678): var1% = 15.28 var2& = -2000000000 var3# = 12345678.12345678# PRINT var1% PRINT var2& PRINT var3# Output: 15 -2000000000 12345678.12345678

Subroutines and functions
A subroutine (also called a "module") is a "mini-program" inside your program. In other words, it is a collection of commands--and can be executed anywhere in your program. To create a subroutine: 1. Go to the "Edit" menu 2. Select "New Sub" 3. Enter a name for the subroutine 4. Type a list of commands between SUB and END SUB To use the subroutine: 1. Press F2 2. Select "Untitled" 3. Press Enter to return to the "main module" 4. Use CALL to execute the subroutine

TIP: Another way to create a subroutine is by typing SUB in the main module. SUB MySub

The following example does not use subroutines: PRINT "Enter some text:"; INPUT text$ PRINT "The text you entered was: "; text$ PRINT "Enter some text:"; INPUT text$ PRINT "The text you entered was: "; text$ PRINT "Enter some text:"; INPUT text$ PRINT "The text you entered was: "; text$ PRINT "Enter some text:"; INPUT text$ PRINT "The text you entered was: "; text$ PRINT "Enter some text:"; INPUT text$ PRINT "The text you entered was: "; text$

PRINT "Enter some text:"; INPUT text$ PRINT "The text you entered was: "; text$ PRINT "Enter some text:"; INPUT text$ PRINT "The text you entered was: "; text$ By using a subroutine, the above program can be simplified like this: CALL CALL CALL CALL CALL CALL CALL GetText GetText GetText GetText GetText GetText GetText

SUB GetText PRINT "Enter some text:"; INPUT text$ PRINT "The text you entered was: "; text$ END SUB The following is even more concise: FOR x = 1 TO 7 CALL GetText NEXT

SUB GetText PRINT "Enter some text:"; INPUT text$ PRINT "The text you entered was: "; text$ END SUB

Parameters
Parameters are numbers and strings that you pass to a subroutine, much like a QBasic command.

' This passes 16 as a parameter: CALL OutputNumber(16)

' Notice the parentheses around the parameter "num." ' Any variables placed inside the parentheses are set as

' the subroutine's parameters. SUB OutputNumber (num) PRINT num END SUB Output: 16

TIP: Variables created in your program cannot be used in the subroutines unless you use COMMON SHARED (followed by a variable) in the main module. COMMON SHARED x$

Functions
A function is the same as a subroutine, except it returns a value. Also, you must leave out the CALL command. To return a value, set a variable with the same name as the function. PRINT Add(10, 7)

FUNCTION Add (num1, num2) Add = num1 + num2 END FUNCTION Output: 17 Since a function can return a value, the name of the function can end with special characters (see Variable types, Using special characters). ' Notice the dollar sign ($) after "Add." It means ' the function returns a string. PRINT Add$("Hello", "World")

FUNCTION Add$ (str1$, str2$) Add$ = str1$ + str2$

END FUNCTION Output: HelloWorld

Numbering systems
(This chapter is provided to help you understand certain parts of chapter 19, Memory.) Normally, when we use a number such as 110, we understand it to mean "one hundred and ten," but in this chapter you will see how this is not always the case.

Hexadecimal numbers
We generally use the base 10 (decimal) numbering system, where each digit must be between 0-9; but the "hexadecimal" system (base 16) can also have digits A, B, C, D, E, and F (16 total digits). (The hexadecimal numbers in this tutorial are red.) 0 1 2 3 4 5 6 7 8 9 A B C D E F = = = = = = = = = = = = = = = = Zero One Two Three Four Five Six Seven Eight Nine Ten Eleven Twelve Thirteen Fourteen Fifteen

In the base 10 system, you add another digit when you get past the number 9; but with base 16, it isn't added until after F (or fifteen). 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 = = = = = = = = = = = = = = = = = Sixteen Seventeen Eighteen Nineteen Twenty Twenty one Twenty two Twenty three Twenty four Twenty five Twenty six Twenty seven Twenty eight Twenty nine Thirty Thirty one Thirty two

21 22 23 24 . . .

= = = =

Thirty Thirty Thirty Thirty

three four five six

In the decimal system (base 10), we multiply ten for each time a digit goes to the left. 10 100 1000 10000 . . . = = = = 10 10 * 10 10 * 10 * 10 10 * 10 * 10 * 10

But in the hexadecimal (base 16) system, we multiply sixteen, instead. 10 100 1000 10000 . . . = = = = 16 16 * 16 16 * 16 * 16 16 * 16 * 16 * 16 (16) (256) (4096) (65536)

Therefore, since 10 is 16 and 100 is 256, the number 110 is two hundred and seventy two (272). 110 = (100 + 10) = (256 + 16) = 272 (To download a number converter, click here.)

TIP: To enter a hexadecimal number in QBasic, use &H. &H110

Binary numbers
The "binary" system (base 2) can only have two digits, 0 and 1. Therefore, no binary number has a digit between 2 and 9.

(Binary numbers are shown in dark blue.) 0 1 10 11 100 101 110 111 1000 1001 1010 1011 1100 1101 1110 1111 10000 10001 10010 10011 10100 . . . = = = = = = = = = = = = = = = = = = = = = Zero One Two Three Four Five Six Seven Eight Nine Ten Eleven Twelve Thirteen Fourteen Fifteen Sixteen Seventeen Eighteen Nineteen Twenty

Notice how binary numbers can be found by excluding numbers that have a 2, 3, 4, 5, 6, 7, 8, or 9. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 . . .

97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 . . . In base 10, as explained above, we multiply ten for each time a digit goes to the left. 10 100 1000 10000 . . . = = = = 10 10 * 10 10 * 10 * 10 10 * 10 * 10 * 10

But in binary, we multiply by two. 10 100 1000 10000 . . . = = = = 2 2 * 2 2 * 2 * 2 2 * 2 * 2 * 2 (2) (4) (8) (16)

So, since 10 is 2 and 100 is 4, the number 110 is six. 110 = (10 + 100) = (2 + 4) = 6 (To download a number converter, click here.)

TIP: Binary (and hexadecimal) numbers are often written with leading 0's. 0000 0001 0010 0011 (same as 0) (same as 1) (same as 10) (same as 11)

Memory
(Before you study this chapter, you may need to read chapter 18, Numbering systems.)

Bits
A "bit" is the smallest piece of data stored in your computer's memory. The value of a bit can be either 0 or 1. All data in your computer has a certain number of bits.

Bytes
A "byte" is 8 bits, and can have a value between 0 and 255 (or, in binary, between 0 and 11111111). A character, such as Q, takes up one byte of memory. This is because there are 256 different characters. (If you don't fully understand bits and bytes, don't worry about it.)

How data is stored
Data is stored in RAM at a certain memory address, as explained in chapter 3 (Variables). Each address takes up 1 byte of memory. Therefore, it can only have a value between 0 and 255. A memory address (on a 32-bit computer) can be somewhere between 0 and 4,294,967,295. In hexadecimal, this is between 0 and FFFFFFFF. Each memory address is divided into two parts: segments and offsets. See the figure below.

Segments and offsets

A memory address such as 12345678 (in hexadecimal) has a segment of 1234 and an offset of 5678. A segment can have a value between 0 and 65535 (or between 0 and FFFF). An offset can be within the same range. You can find out a memory address of a piece of data by multiplying its segment by 65536 (or 10000, in hexadecimal) and then adding its offset to the result. In QBasic, you can get a variable's segment by using VARSEG and its offset by using VARPTR. segment = VARSEG(x) offset = VARPTR(x) ' This prints the memory address of "x" (in decimal): PRINT (segment * 65536) + offset