Software to merge shop and online shop items?

-I just opened my shop and I wild like to open a site where I sell my goods but I want a software "point of sale" that can do this job for me, let us say that I have 10 items in the shop and the same number of the items in the shop site too, but if some of my customer buy 2 items from my shop therefore I want these two items to be "out of stuck" in my site throughout the software and the same goes if someone buy items from the site



I hope my point is clear and sorry for my poor English =)