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

Examples:

1.  a = 15 / 4 + 3
    PRINT a
    Result on the screen – 6

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: 22
Computer: Enter the second number
You: 18
Computer: 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)	(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 executes if the
PRINT "but"; a; "-"; c; "="; e      result of a / b is not integer
PRINT "and"; e; "/"; b; "="; f; " - 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!