problem with Ceiling

Hi,

I am facing problem on executing ceiling function.

when i am giving B=3.0 and c=ceiling(B) it.gives correct result 3

But when i am getting B by some calculations and execute for c it gives incorrect result.

    like B=(dx-2*via_enc)/via_pitch

          c=ceiling(B)

    it gives B=3.0 and c=4.

What can be the cause of this error?

Thanks