The assignment operator is called when an already created object is assigned to the value of another one. By default, you will get a copy assignment operator that will copy all the data members. This is not necessarily what you want, particularly if the object has a data member that is a pointer, in which case your intention is more likely to do a deep copy and copy the data pointed to rather than the value of the pointer (in the latter case, two objects will point to the same data).
If you define a copy constructor, you will still get the default copy assignment operator; however, it makes sense that if you regard it important to write your own copy constructor, you should also provide a custom copy assignment operator. ...
