Error: cannot dynamically allocate this value type object on native heap - c++-cli

Question

I am trying to create an instance of System::DateTimeon-the-fly and assign it to System::DateTime gDate in case user uses 'P' argument. But, I get the error shown following the code snippet.
case 'P':
gDate=new DateTime(std::stoi(year), std::stoi(month), std::stoi(day));
cout << "Persian Date is: " << pDate.GetDayOfMonth(gDate) << "/" <<
pDate.GetMonth (gDate) << "/" << pDate.GetYear(gDate) << endl;
break;
Error C3255 'System::DateTime': cannot dynamically allocate this value
type object on native heap
What causes the error and how should I prevent it?
Update:
I probably should have said in the first place, I tried also the following definition:
DateTime gDate(std::stoi(year), std::stoi(month), std::stoi(day));
But, I received the error, Error C2360 initialization of 'gDate' is skipped by 'case' label

Answer 1

If you don't need gDate to be a pointer, and you almost certainly do not, try:
case 'P':
{
DateTime gDate(std::stoi(year), std::stoi(month), std::stoi(day));
cout << "Persian Date is: " << pDate.GetDayOfMonth(gDate) << "/" <<
pDate.GetMonth (gDate) << "/" << pDate.GetYear(gDate) << endl;
}
break;
The braces establish a scope for gDate, ensuring deletion when the program exits the braces.
CLI/CLR C++ is a different beast from C++ and has some different semantics.
CLI/C++ has added a concepts of value and ref structs and classes. These are objects with automatic lifetime control. The .Net runtime, not the programmer, decides when they live and die, and this requires different syntax.
Those tagged value are intended to be used as one would use a Plain Old Datatype like an int or a double. Create 'em as a temporary, use them, and let the stack or whatever other method of managing temporary variables is in use take care of the clean-up. You can point to them, but it is not recommended.
ref structs and classes are designed with referenced use in mind and are open game for pointers, so long as they are garbage collected pointers.
System::DateTime is a value struct, so what follows strays from its recommended use. As a pointer, System::DateTime must either be used as a garbage collected pointer with ^ in place of * and allocated with gcnew in place of new or as a variable with a defined scope.
If gDate must be a pointer, it must be defined
DateTime ^ gDate;
And allocating it requires
gDate = gcnew DateTime(std::stoi(year), std::stoi(month), std::stoi(day));
When there are no further references to this allocated object, gDate and any copies of gDate have gone out of scope, the .Net runtime's garbage collector will destroy it.

Answer 2

As explained here, you can create DateTime on the stack, but not on the heap.
Try like this:
DateTime gDate(std::stoi(year), std::stoi(month), std::stoi(day));
cout << "Persian Date is: " << pDate.GetDayOfMonth(gDate) << "/" <<
pDate.GetMonth (gDate) << "/" << pDate.GetYear(gDate) << endl;
break;
alternatively, you can use gcnew to allocate managed memory:
DateTime^ gDate = gcnew DateTime(std::stoi(year), std::stoi(month), std::stoi(day));