'===========================================================================
' Subject: GREATEST COMMON DIVISOR (GCD)      Date: 11-24-98 (22:29)       
'  Author: Jeff Connelly                      Code: QB, QBasic, PDS        
'  Origin: shellreef@email.msn.com          Packet: ALGOR.ABC
'===========================================================================
' Created:09-22-98
' By Jeff Connelly

' Calcuates the greatest common factor (GFC) of two numbers

REM $DYNAMIC        ' Dynamic array resizing

' These arrays initally contain only one element, will be REDIMed
DIM aa&(0)
DIM ab&(0)

INPUT "Factor array size: ", size
REDIM aa&(size)
REDIM ab&(size)

INPUT "First number: ", a
INPUT "Second number: ", b

' Build the array of factors
PRINT "Calculating factors of "; a; " and "; b; "..."
free = UBOUND(aa&)
FOR i = 2 TO a - 1
    IF ((a / i) = INT(a / i)) THEN
        IF (free > UBOUND(aa&)) THEN EXIT FOR
        aa&(free) = i
        free = free - 1
    END IF
NEXT
free = UBOUND(ab&)
FOR i = 2 TO b - 1
    IF ((b / i) = INT(b / i)) THEN
        IF (free > UBOUND(ab&)) THEN EXIT FOR
        ab&(free) = i
        free = free - 1
    END IF
NEXT

FOR i = UBOUND(aa&) TO 0 STEP -1        ' go backwards
    IF (aa&(i) = 0) THEN EXIT FOR
    FOR j = UBOUND(ab&) TO 0 STEP -1
        IF (ab&(j) = 0) THEN EXIT FOR
        IF (aa&(i) = aa&(j)) THEN PRINT "GCF found: ", aa&(i): SYSTEM
    NEXT
NEXT

PRINT "GCF not found, increase array size."