RosettaCodeData/Task/Greatest-common-divisor/QuickBASIC/greatest-common-divisor-2.basic

DECLARE FUNCTION gcd (a%, b%)
PRINT gcd(30, 18)
END

FUNCTION gcd (a%, b%)
  IF b% = 0 THEN
    gcd = ABS(a%)
  ELSE
    gcd = gcd(b%, a% MOD b%)
  END IF
END FUNCTION