Click the flag and enter a pokemon type, then another that's not the same. This prgram will generate a dual type and output the type's matchups. I've included a type chart so you can check for yourself. I had to enter the weaknesses and resistances for each individual type manually, so there's a tiny chance I messed up somehwere.
I've started work on a pokemon fangame and I decided to start with some important mechanics. If you go to see inside you can see some other stuff I was fooling around with.
