What is the datatype of the pinMode function? I just tried it, but the Arduino IDE crashed, I hope its not related.
I want to declare a datatype like this:

int a = pinMode(pin, OUTPUT);


or something like that, but I'm not sure what datatype the pinMode function uses. I looked on the pinMode documentation page, of the Arduino website, and I see basic usage, but not a more clear definition of the source code for that function.
pinMode(pin, Mode); is a void. It doesn't return anything. It simply sets a pin as an OUTPUT or an INPUT.
It says it in the link you posted.

Returns
None

That means that the function doesn't return any value.