QBasic Tutorials: QBasic for Beginners - Chapter 2

Chapter II

Mathematical Calculations

QBasic was obviously created for us to have fun, play games, draw nice graphics and even make sounds. But, as you might guess, nothing good comes without a bit of effort that has to be put in it. In the most QBasic programs a bit of math has to be done. The math… Doh! If you hate mathematics, don’t worry. Qbasic will do it all for you, you just need to know how to tell QBasic to do that.
Qbasic can perform the following mathematical operations:

Operator What it does Example Result
+ Add 7 + 2 9
- Subtract 7 - 2 5
* Multiply 7 * 2 14
/ Divide 7 / 2 3.5

Example 1:

a = 15 / 4 + 3
PRINT a

Result on the screen:

6

Example 2:

PRINT "Enter the first number"
INPUT a
PRINT "Enter the second number"
INPUT b
c = a + b
d = a * b
PRINT a; "+"; b; "="; c
PRINT a; "*"; b; "="; d
END

When you run this program it goes like this:
Computer:

Enter the first number

You:

Enter the first number 22

Computer:

Enter the first number 22
Enter the second number

You:

Enter the first number 22
Enter the second number 18

Computer:

Enter the first number 22
Enter the second number 18
22 + 18 = 40
22 * 18 = 396

Advanced operations:

Operator What it does Example Result
\ divides and turns the result into
an integer(the whole number)
7 \ 2 3
^ Raises a number to the
power of another number
3 ^ 4
(means: 3*3*3*3)
2.5 ^ 3
(means: 2.5*2.5*2.5)
 
243
 
15.625
SQR Calculates the square root
of a number
SQR(9)

SQR(16)

SQR(5)
3
(because: 3^2=9)
4
(because: 4^2=16)
2.236
MOD Divides two numbers, and if the
result is not an integer
(for example - 3.25), finds out
how much to subtract from the first
number in order to get the
integer result.
17 MOD 5 2
(because: 17 / 5 = 3.4
17 – 2 = 15
15 / 5 = 3)

The following program explains MOD. Type this program (except my comments) into Qbasic accurately and run it to see how MOD works.

1 CLS 'this command clears the screen, so it’s empty
INPUT "Enter the first number "; a
INPUT "Enter the second number "; b
IF b = 0 THEN 'checks if the second number is zero,
'because you can’t divide by zero
PRINT "the second number cannot be 0. Try again."
DO: LOOP WHILE INKEY$ = "" 'waits for you to press a key to continue
GOTO 1 'then sends you back to line 1
END IF
CLS 'clear the screen again
c = a MOD b
d = a / b
e = a - c
f = e / b
PRINT a; "MOD"; b; "="; c
IF c = 0 THEN 'this checks if the result of a MOD b = 0, because
'it means that the result of a / b is integer
PRINT "because"; a; "/"; b; "="; d; " - integer. Try again."
DO: LOOP WHILE INKEY$ = "" 'waits for you to press a key to continue
GOTO 1 'then sends you back to the line 1
END IF
PRINT "because"; a; "/"; b; "="; d; " -not integer" 'The rest of the program
PRINT "but"; a; "-"; c; "="; e 'executes if the result of
PRINT "and"; e; "/"; b; "="; f; " - integer" 'a / b is not integer
END

This program may look very complicated for you, but don’t worry. Qbasic is a very easy language to learn and soon you’ll be having fun with it. I promise you!