Logic gate help Answered

I'm attempting to build an binary calculator out of an old iphone box using LED's and such and have a wiring system set up but i need to know how to make/buy some form of "if then else" gate (i.e. if A=1 then B=1 else C=1 and if A=0 then B=0 and C=1). I would love to know if there is some kind of way to do this using transistor logic but anything that works as an "if then else" gate is welcome.