A few examples of different loops,
loopy: DO i = 1, 30, 2 ... ! 15 iterations END DO loopy
DO j = 30, 1, -2 ... ! 15 iterations END DO
DO k = 30, 1, 2 ... ! 0 iterations ... ! loop skipped END DO
DO l = 30,1 ... ! zero-trip loop END DO
For more information, click here