You can't call a class. You can create instances of a class and call its member functions.
Since you have not specified which constructor to be used to initialize the objects in P it will try to use the default constructor (constructor that takes no arguments). Point doesn't have a default constructor so that's what the error message "no matching function for call to Point::Point()" is about.
Either create a default constructor or specify the constructor in the constructor initialization list.
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To make line 26-28 compile you would have to define operator(int, int) as a member of Point.