what is sign for the height of the object and image in case of both concave and convex lens.give whether it is+ ve or - ve

Dear student,
Heights measured upwards and perpendicular to the principal axis are taken positive.
Heights measured downwards and perpendicular to the principal axis are taken negative. 
The object height h is always positive. Height h' of virtual erect image is positive and that of real inverted image is negative.
The linear magnification, m = h'/h is positive for a virtual image and negative for a real image.


Regards