Category : BASIC Source Code
Archive   : QBFAQR01.ZIP
Filename : ERATOS.BAS

'Date: 03-23-92 (22:35)
'From: BRENT ASHLEY
'---------------------------------------------------------------------------
'Here's a variation on a program I entered in a primes contest about a
'year ago.


DEFINT A-Z
' initialise array to zeros
DIM flags(10000)

max = 10000
rootmax = SQR(max)
NonPrime = -1

' show 2 as prime
PRINT " 2 ";

' flag all non-primes
FOR Num = 3 TO rootmax STEP 2

' check for prime
IF NOT flags(Num) THEN

' print prime number
PRINT USING " ###### "; Num;

' flag all multiples
multiple = 2 * Num
WHILE multiple <= max
flags(multiple) = NonPrime
multiple = multiple + Num
WEND
END IF

' flag even numbers
flags(Num + 1) = NonPrime
NEXT

END ' of program