The reason why you should use the : Object(data) in the constructor is because there is a difference between initialization and assignment.

consider this:
int a = 2; // 1
int b; // 2a
b = a; // 2b

Line 1 is initialization. Line 2a is also initialization, it just is created with a default value. The default value random junk in this case (although some compilers, in debug mode, initialize it to 0 it is not guaranteed). And line 2b is assignment.

Why does this matter? When you make your own objects. Lets say you created an object alpha which has a constructor like this:



Then if you made object beta contain an instance of beta, you Have to initialize it because there is no default constructor. That is to say, this won't compile:because by the time the code execution gets to the block ( {} ) all constructors have been called. From now on you can only assign to to the objects. The way c++ gets around this is by using the 'initialization list' described by Antheus. Hope that helps.