Tracking Turns in Turn Based Game Loop

I’m trying to keep track of what number turn it is in this turn based game I’m building. The game focuses a lot on simulation, and is expected to run for weeks, months, possibly years. Each “turn” occurs roughly every ten seconds. Ideally, I want to be to able to check data for what happened on what turn, and thus I need to keep track of turn number.

With this in mind, what kind of data type should I use to keep track of what numbered turn it is? I’m thinking ulong but is there a better way to handle this then just tracking a ulong variable?

Arkaid’s comment answers my question.