Mesa Community College - Business Administration Department - Computer Information Systems (CIS) - 2000
This QBASIC Getting Started exercise is designed to help students access and use Microsoft’s QuickBASIC (QBASIC).
QBASIC is Microsoft’s version of the BASIC (Beginner’s All-purpose Symbolic Instruction Code) programming language.
QBASIC was developed for MS-DOS, so the interface is not as intuitive as most software packages developed for Windows,
thus a need for a simple exercise, which can then be used as a reference when completing lab assignments. Instructions on how
to enter, save, execute, print, and retrieve a program are covered. This exercise does not cover program design, development,
QBASIC syntax, and QBASIC commands. However, a list of QBASIC commands is provided to support any other
instructional material that may be used. Statement Description Example CLS Clears the screen CLS DO WHILE / LOOP Used to form a do-while loop DO WHILE x < 10 END Last statement to mark the end END GOSUB label Branch to a subroutine; subroutine is identified by its label:. GOSUB INPUT.RTN See the RETURN statement. RETURN Return to the statement right after the GOSUB that branched the processing to this routine INPUT.RTN: IF-THEN-ELSE-ENDIF Conditional branching IF x < 10 THEN INPUT Enables data to be entered interactively INPUT "Enter hourly rate: "; hr LET Assign a value to variable LET sum = num1 + num2 PRINT Displays information PRINT "The sum is "; sum READ Assigns values to variables from a list of DATA statements READ num1, num2 DATA Batch data within the program DATA 8, 16 REM Remark REM This program adds 2 numbers RESTORE Moves data pointer to first DATA statement RESTORE Statement Description Example CALL Calls a subroutine CALL calc.rtn (num1, num2) CLOSE Closes a file CLOSE #1 DEF Sets up a user-defined function DEF FNC(n1,n2) = n1 + n2 DIM Dimensions an array DIM X(12) DO / LOOP UNTIL Used to form a do-until loop DO FOR / NEXT Used to form a FOR-NEXT loop FOR x = 1 to 10 FUNCTION / Used to define a function procedure FUNCTION area (num1) INPUT #n Reads data from a sequential file INPUT #1, num1, num2 ON x GOSUB Branches to a specific label based on the value of the variable ON x GOSUB rtn-1, rtn-2, rtn-3 OPEN file FOR OUTPUT AS #n Opens an external file for input or output and assigns a numeric value for internal reference (#1, #2, #3, etc) OPEN "A:out_file" PRINT USING x$ Use to display formatted output S$ = "sum is ####.##" SELECT CASE Branches to a specific case SELECT CASE num1 SUB / END SUB SUB calc.rtn (num1, num2, sum) WRITE #n Writes data to a sequential file WRITE #1, num1, num2, sum
Accessing QBASIC:
Click on Start and follow the following menu path:
Start > Classes > Structured Classes > CIS105 > QBASIC
Press ESC to enter the QBASIC editor
QBASIC Editor:
In a full installation, there is some online help available. Each time QBASIC is executed, the option of entering the
Survival Guide is presented. Simply press ESC to clear the dialog box and enter the QBASIC editor. Although
QBASIC is not a Windows program, it provides menus as well as shortcut keystrokes. A combination of these
are used throughout the exercise as the practice program is entered.
Once in the editor, enter the following simple program to practice using QBASIC.
Press the Enter key at the end of each line.
REM This program adds two numbers and prints the sum
CLS
READ num1, num2
LET sum = num1 + num2
PRINT “The sum is ”; sum
DATA 8,16
END
Saving Programs:
Before continuing, the program should be saved. In most cases, the program will be saved on the floppy drive (A:).
Click on File and select Save As. Enter A:PRACTICE as the filename, and then click
on OK. Leave the QuickBASIC format option selected. QBASIC automatically assigns an extension of .BAS.
Executing Programs:
After entering the program, you are ready to execute it. When you execute it, QBASIC will first check the
program for syntax errors. If any errors are identified, correct the errors and try executing it again. Click
on Run and select Start to execute the program, or press the function key F5 on top of the keyboard.
In the example that follows, the READ statement was changed to RED to cause a syntax error. As depicted
below, the error message is not very helpful, but at least the word RED is highlighted. This gives you an idea
of where the error is. For this error, we would click on OK, change RED to READ, and then press F5 again.
If another error existed, then the next time we ran it, that error would be highlighted. The BASIC interpreter
reads the program one line at a time and stops either when it finds an error or it gets to the end of the program.
Sometimes a program needs to be terminated by the programmer before it reaches the end. This usually
happens when the programmer makes an error and codes an endless loop, which means the program will
run forever. Use Ctrl + Break to terminate a program before it reaches its normal ending point.
When a program runs successfully, the output is displayed in a DOS window. At the end of the program execution,
press any key to continue and return to QBASIC.
Printing Sample Output:
If a copy of a program’s output is required, you’ll need to capture a picture of the window by pressing
Alt + Print Screen. The Print Screen button is on top of the keyboard, just to the right of the
F12 key. The picture of the window can then be pasted into and printed from WordPad,
Word, or similar wordprocessor.
Another option is to change the PRINT command to LPRINT. LPRINT sends the output to the device
assigned to LPT1. The use of LPRINT is not recommended especially if there is a chance of
having a print command within an endless loop. This is a problem because once the output is sent to a
network printer, the user can not stop it.
Students should place their name in a REM and PRINT statement. This will help identify printed copies
among the similar programs being printed by other students.
Copying Sample Output:
The text displayed in the output window can also be selected, copied, and pasted into a wordprocessor,
instead of taking a picture of the window. In the output window, click on the selection button
,
click and drag around the desired text, click on the copy button
,
and then switch to a wordprocessor and paste it. This is effective when multiple pages of output should
appear as one page. The catch is that the programmer needs to ensure that no more than 23 lines of
output are displayed at one time, and that an input prompt is added to pause the program’s execution.
During the pause is when the output should be captured. Review lab assignments #2 and #3 provided
on a separate document to see this technique employed.
Printing Programs:
Print the program currently opened by clicking on File and selecting Print.
Within the print option’s dialog window, the correct choice of Current Module
is selected automatically if no text was selected before issuing the print command. Click on
OK or press the enter key to print the program.
Retrieving Programs:
To retrieve your program from the floppy, click on File and select Open Program.
Click on [-A-] under Dir/Drivers. A list of programs should be listed in the Files window.
Only the files with an extension of .BAS are listed. Click on the desired file and click OK.
After retrieving the program, it can be modified and executed again. Be sure to save again it if any changes are made.
Exiting QBASIC:
To exit QBASIC click on File and select Exit. Be sure to save before exiting.
QBASIC Commands - Level I:
.
QBASIC statements
.
LOOP
.
QBASIC statements
.
RETURN
LET y = 5
ELSE
LET y = 10
ENDIF
QBASIC Commands - Level II:
.
QBASIC statements
.
LOOP UNTIL x < 10
.
QBASIC statements
.
NEXT x
END FUNCTION
.
QBASIC statements
.
END FUNCTION
FOR OUTPUT AS #1
or
OPEN "A:in_file"
FOR INPUT AS #1
PRINT USING S$; sum
CASE 1, 2, 3, 4,
PRINT "LOW NUMBER"
CASE ELSE
PRINT "HIGH NUMBER
END SELECT
.
QBASIC statements
.
END SUB