Оператор if...then - QBasic

' ...
IF (a < 0 AND b < 0 AND c = 0) OR (a < 0 AND b = 0 AND c < 0) OR (a = 0 AND b < 0 AND c < 0) THEN
PRINT TAB(10);
PRINT "Zadannye chisla nepolojitelnye"
END IF
IF (a = 0 AND b = 0 AND c < 0) OR (a = 0 AND b < 0 AND c = 0) OR (a < 0 AND b = 0 AND c = 0) THEN
PRINT TAB(10);
PRINT "Zadannye chisla nepolojitelnye"
END IF
' ...