Why use classes when the same can be implemented using structures?
Reasonable question. For starters, structures in C could not work like classes. Classes were needed to implement object-oriented programming. Then it looks like the designers of C++ decided they might as way give the class functionality to structures as well (which are similiar to classes).
I don’t know all the thinking that went into that, but the two are very similar. The primary difference is that, by default, structure members are public (can be accessed by code that references the structure), while class members are private (which is more in line with the OOP approach).