菜鸟！！winform程序中如何在头文件中定义函数

函数void ShowAAA()
{
edit->text="AAA";
}

上面这段代码声明应该放在哪里，实现放在哪里？？






//unit1.cpp-------------------------------------------------

#include <vcl.h>
#pragma hdrstop

#include "Unit1.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TMainForm *MainForm;
//---------------------------------------------------------------------------
__fastcall TMainForm::TMainForm(TComponent* Owner)
        : TForm(Owner)
{
}
//---------------------------------------------------------------------------
void __fastcall TMainForm::btnSunClick(TObject *Sender)
{

}
//---------------------------------------------------------------------------

//--------------------------------------------------------------------
unit1.h

class TMainForm : public TForm
{
__published:    // IDE-managed Components
        TButton *btnSun;
        TEdit *txt1;
        void __fastcall btnSunClick(TObject *Sender);
private:    // User declarations
public:        // User declarations
        __fastcall TMainForm(TComponent* Owner);

};
//---------------------------------------------------------------------------
extern PACKAGE TMainForm *MainForm;
//---------------------------------------------------------------------------
#endif