[heena.mca]

Is there any difference between List x; and List x();?

[asadullah.ansari]

if List is class
then meaning of List x is that x is object of class List.
meaning of List x() is that x is a function which returns a object type List.

[ismail.tech21]

you can see the following example

void f()
 {
   List x;     // Local object named x (of class List)
   ...
 }

 void g()
 {
   List x();   // Function named x (that returns a List)
   ...
 }