Copy Constructor and Assignment operator

The assignment operator is used to copy the values from one object to another "already existing object".

Eg:    classA objectone(5); //Calls classA constructor.
         classA objectTwo;    //Calls classA default constructor.
         objectTwo = objectone; // Calls classA assignment operator.

• In this case,objectTwo has already created by the time assignment is executed.consequently the classA assignment operator is called.

If the object is being copied into does not exist then "copy constructor" comes into existence.

Eg:
       ClassA object1(5) ; //calls classA constructor,
       ClassA object2 = object1;//Calls classA's copy constructor.

A "Copy constructor " is a special constructor that initializes a new object from an existing object.

• The assignment operator copies to existing objects,and the copy constructor copies to newly created objects..
• If a new object has to be created before copying can occur,the copy constructor is used.

Where we need "Copy constructor" : 

• When instantiating one object and initializing it with values from another object.
• When passing an object by value.
• when an object is returned from a function by value.