error C2065: 'WCHAR' : undeclared identifier

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C++

i created the header file

//header file
class CReadSubstitute  
{
	protected:
	
		CReadSubstitute();
		virtual ~CReadSubstitute();
		void GetNextWord(WCHAR * szWord);
		void Substitute(WCHAR* szWord);
		void SetFont(LPSTR szFontName);
		void GetFont(LPSTR szFontName);

	private:
		xehandle m_xehndl;
		int32 m_start;
		int32 m_end;
		int32 m_textlen;
		int32 m_LoopCounter;
		int32 m_selWordStart,m_selWordEnd;
};

now i created one .cpp file

class CReadSubstitute; //this is the forward declaration 

now i want to use the function 

CReadSubstitute::GetNextWord(WCHAR * szWord)
{
     //code 
}

but it is giving errors

error C2065: 'WCHAR' : undeclared identifier
error C2065: 'szWord' : undeclared identifier
error C2448: '<unknown>' : function-style initializer appears to be a function definition

can some1 tell what is the prob.
i also included the header file in .cpp