when should I use the new operator in C++

Question

Say I have a class called Money which has parameters Dollars and Cents

I could initialize it in the followings 2 ways:

Answer 1

Money a(3,15);

Allocates an Money object in the local scope.

Money* b=new Money(3,15);

Allocates a pointer-variable to the local scope, and makes the pointer "point" to a Money object that resides in the free store (assuming the allocation completed successfully, otherwise an std::bad_alloc() is thrown)

Example 1 :

Assume next scenario:

Money * b = initialize();

where

Money* initialize()
{
      Money x(2 , 15);
      return &x;
}

This will fail because after initialize() reaches the end of execution x is destroyed, and now b points to a location that is invalid to use and invokes Undefined Behaviour if you do used it. so instead you should allocate it with a pointer

Money* initialize()
{
      return new Money(2,15);
}

The free-store is also used when you want to store and use arrays of great size.

There is a difference between the two as you noticed on the example, and that is that in the local scope x you do not need to delete the object. But when using new you will have to manually do a delete x;. Otherwise a memory leak (memory space is occupied without ever going to be used again, hence eating memory) is occurring.

See Martin York's answer for deeper knowledge beyond this post.