Pixel perfection problems

I fairly new to Illustrator and I am trying to make pixel perfect icons. My problem is that When I make for example a triangle, it will first show W: X H X but then later for example W: X.4321and H: X.1234. Even I am pretty sure that I did not touch it.

Is there away to make illustrator not to even make such decimals? I've tried my best to look for pixel perfection tutorials but I don't know if there is a good answer for that. I've checked the boxes 'align to grid' etc.  Can I force Illustrator not to use decimals at all?

Also my grid likes to put stuff middle of those little squares in the grid and say that it is for example X: 16 and Y: 16 and not X: 16.5 and Y: 16.5 as it would seem to me. And sometimes there is no such problem. What am I missing?