#include <iostream>
#include <string>
 
class Foo
{
public:
       std::string sayHello()
       {
         return "Hello";
       }
};
 
int main()
{
    Foo test;
    std::cout << test.sayHello();
 
    std::cin.get();
}

string classname;
std::cin >> classname;
(it's invalid but...)  classname * cn = new classname();
 

if(classname == "Foo")
     Foo * foo = new Foo();
elseif(classname  == "Bar")
     Bar * bar = new Bar();
...

class Foo
{
   public Foo() { }
};
 
int main()
{
    string className = "Foo";
    Foo * foo; //not instantiated but waiting in a sense to be created.
 
    if( className == "Foo")  //a string variable has the class name FO
       foo = new Foo(); //so create a new class of that object
 
   //after foo is done being used with
  delete foo;
}