error LNK2019 in visual studio 2008 express

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C++

I have just started to try to create my own library of functions in c++, using vs2008 express.

I know this is probably a simple problem to the experts out there but I started with a simple test example to see if I could manage.

I have put the paths to my include and library files into the ide compiler.
Any advice on what I have done wrong will be appreciated. Thanks in advance

I have included the code if this helps: (For some reason the submitted question has omitted #include <iostream>)

This is the error message:
1>functest.obj : error LNK2019: unresolved external symbol "int __cdecl twicenum(int)" (?twicenum@@YAHH@Z) referenced in function _main
1>C:\Users\Bill\Documents\Visual Studio 2008\New folder\testfunclib\Debug\testfunclib.exe : fatal error LNK1120: 1 unresolved externals

code for main (1), header (2) and function definition (3) modules follows:
................................................................................................(1)...
//main prg is called testfunclib
..........

#include <iostream>
#include "myfunclib.h"
using namespace std;
int main()
{
int b=twicenum(4);
cout<<b;
}

.....(2)....................................................................................
Header File myfunclib.h

//… Namespaces, variables, and function prototypes go here




/*You have to put extern before your prototyped function you want to use in your library*/


extern int twicenum(int);



(3).............................................................................................
function definition twicenum.cpp

#include "myfunclib.h"
#include <iostream>
using namespace std;


int twicenum(int x);
{
int res;
res=x*2;
cout<<res;
return (res);
}




........................................................................................