Build DLL with Visual studio problem

Hi there, I'm trying to build a dll with C++ and I followed this tutorial: http://msdn.microsoft.com/en-us/library/ms235636(v=vs.100).aspx  In the article it says, "By default, MATHFUNCSDLL_EXPORTS is defined when your MathFuncsDll project is built." I wrote this trial code: (trialDLL.h)

#ifndef TRIALDLL_H_
#define TRIALDLL_H_

class MyMathFuncs
{
private:
	double offset;

	double getOffset();

public:
	MyMathFuncs(double offset);

	double Add(double a, double b);

	double Multiply(double a, double b);
};

#ifdef __cplusplus
extern "C"{
#endif

#ifdef TRIALDLL_EXPORT
#define TRIALDLL_API __declspec(dllexport)
#else
#define TRIALDLL_API __declspec(dllimport)
#endif

	MyMathFuncs* __stdcall TRIALDLL_API new_MyMathFuncs(double offset);

	double __stdcall TRIALDLL_API MyAdd(MyMathFuncs* myMath, double a, double b);


#ifdef __cplusplus
}
#endif


#endif

And its corresponding definition .cpp file. But when I build it, using visual studio 2010 ultimate, building failed and gives error: trialdll.h(29): error C2059: syntax error : '__declspec(dllimport)' and  (the same problem) error C2059: syntax error : '__declspec(dllimport)'. I wonder why is this? If the statement from the tutorial is true, TRIALDLL_API should have been defined as __declspec(dllexport) in the macro rather than __declspec(dllimport). If the statement is false, can I ask for a solution, possibly how to build it on command line?

Thanks a lot to whomever replies and helps.