PPC stands for Pay Per Click... it is basically pay on ads of clicks you can say it is based on click search engine...
on other hand PTC stands
for paid to click.This is completely different from PPC program. The advertiser will pay the viewer certain amount for clicking and viewing the advertisement.
There is nothing be confuse, it is very clear that what is PPC ,Pay Per Click or can say pay for per click to Google or other Search engines which is campaign PPC to their affiliates on the other hand PTC is Pay To Click it is the service provided by some web site which has affiliate mean that PTC service provider is behave like a middle man or can say broker and you have to pay to PTC service provider for per clicks and it can be fraud mostly.
Mostly PTC service provider has a mini site network and some fraud user to click frequently with different IP's and locations so personally I think PTC is not good now I want to know your and other webmasters views about it.