Fixing a slab foundation or pouring new
If you've got an older slab with a crack or two, the first question is why it cracked. A thin crack from the concrete shrinking as it dried can usually be sealed and left alone. When the slab has dropped or broken because the soil under it settled, patching the top won't fix what's moving underneath. That's when I'd steer you toward dealing with the ground, either by lifting the slab back up or by tearing out and starting over on packed soil.

