term does not evaluate to a function taking 2 arguments

[Max Pain]

Hi, this is the first c++ program I write on my own. It should be about the RSA algorithm for encrypting data.

The source code is attached. It gives me this error when I try to compile:
error C2064: term does not evaluate to a function taking 2 arguments

The error started when I started to include the euclidic algorithm, nevertheless the euclidic algorithm alone works to compile (and also gives me the gct).

I'm very new to programming (just started three days ago), so please don't blame me if the error is very stupid.

source code attached

every help will be appreciated

thanks