Why won't this work?

Question

Compiler says 2 errors I can't get a grip on them...
The only things other than the example program is that I define the sum function inside the int main part right?
https://code.sololearn.com/cNnXCsDZjRwE/?ref=app

Answer 1

So joining the template line and the int main declaration actually implies that the main function is templates? Cause I was not intended to do that