I'm using Open Watcom IDE. I have been following all the examples/tutorials I have found for creating a Windows DLL. I have very little experience of C programming, could anyone please give me a pointer to what I am doing wrong here?

I have a Hello.c file in my project as:-

Code:
#include <stdlib.h>
#include <stdio.h>
#include <windows.h>

extern "C"
{
    __declspec(dllexport) double GetNumberFromDLL()
    {
        return 50;
    }
}
When I compile I get lots of errors, the first few being:-

"Invalid Declarator" error on the extern
Expecting ';' but found 'C'
Expecting data or function declaration, but found 'string'