Up to you. How many do you want to check for?
Ports are number from 0 upwards. Most PCs will only have one joypad attached, so there's rarely a need to check for any more.
A few may have 2 attached, so check ports 0 and 1 (0 being the default one).
Fewer still may have 4 attached, so check 0 to 3.
Basically, just check for as many as you need to for your game. If it's single player, then you only ever need to check port 0.
Ports are number from 0 upwards. Most PCs will only have one joypad attached, so there's rarely a need to check for any more.
A few may have 2 attached, so check ports 0 and 1 (0 being the default one).
Fewer still may have 4 attached, so check 0 to 3.
Basically, just check for as many as you need to for your game. If it's single player, then you only ever need to check port 0.