[impersonalis]

#include<afxwin.h>
#include<stdlib.h>
#include"resource.h"
//created by imper


class CMyDialog:public CDialog
{
private:
	bool FLAG;
public:
	CMyDialog::CMyDialog():CDialog(IDD_DIALOG1){
		this->FLAG=false;	
	}
	afx_msg void OnPaint();
	afx_msg void ChangeFlag();
	BOOL OnInitDialog();
	DECLARE_MESSAGE_MAP()
};
class CMyApp:public CWinApp
{
public:
	virtual BOOL InitInstance();
};
BOOL CMyApp::InitInstance()
{
	SetDialogBkColor(RGB(192,192,192),RGB(0,0,0));
	CMyDialog dialog;
	m_pMainWnd=& dialog;
	dialog.DoModal();

	return FALSE;
}
BEGIN_MESSAGE_MAP(CMyDialog,CDialog)
ON_WM_PAINT()
ON_COMMAND(IDC_BUT_CHNGFLG,ChangeFlag)
END_MESSAGE_MAP()
BOOL CMyDialog::OnInitDialog()
{InvalidateRect(NULL);


	CDialog::OnInitDialog();


	return TRUE;
}

void CMyDialog::ChangeFlag(){
	this->FLAG=!this->FLAG;
	this->InvalidateRect(NULL);
}

void CMyDialog::OnPaint(){
	CPaintDC dc(this);
	if(this->FLAG){
		dc.TextOut(10,10,"йопта!");
	}

}

CMyApp MyApp;

код жоскей - сам причиши, что нужно