i am trying to repaint the screen in GDI but unfortunately i can''t What is Wrong in This code... NoteMenu item has a Repaint button)

#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <windowsx.h>
#include <mmsystem.h>
#include "resource.h"
#include <stdio.h>
#include <stdlib.h>
#include <time.h>


/////////////////////////////////////CONSTANTS////////////////////////////////////////////////

const char* const WINDOWCAPTION="One of My Windows";
const char* const CLASSNAME="MY CLASS";

//////////////////////////////////////GLOBALS/////////////////////////////////////////////////

int WindowCounter=0;  // Globally tracks Windows

HINSTANCE SparehInstance=NULL; // hInstance of Application


////////////////////////////////////WINPROC//////////////////////////////////////////////////

LRESULT CALLBACK WinProc(HWND hwnd,UINT msg,WPARAM wparam,LPARAM lparam)
{
	PAINTSTRUCT ps;
	switch(msg)
	{
	case WM_CREATE:
		{
			++WindowCounter;
			return 0;
		}
		break;
	case WM_PAINT:
		{
			HDC hdc;
			HBRUSH UsedBrush=CreateSolidBrush(RGB(120,120,120));
			HPEN  UsedPen=CreatePen(PS_SOLID,1,RGB(10,10,10));  
			hdc=BeginPaint(hwnd,&ps);
			GetClientRect(hwnd,&ps.rcPaint);
			Rectangle(hdc,ps.rcPaint.left,ps.rcPaint.top,ps.rcPaint.right,ps.rcPaint.bottom);
			EndPaint(hwnd,&ps);
			ReleaseDC(hwnd,hdc);
			DeleteObject(UsedBrush);
			DeleteObject(UsedPen);
			return 0;
		}
		break;
	case WM_ACTIVATE:
		{
			HDC hdc=GetDC(hwnd);
			char buffer[60];
			SetTextColor(hdc,RGB(220,220,220));
			switch(wparam)
			{
			case WA_ACTIVE:
				{
					sprintf(buffer,"Window is Activated");
					TextOut(hdc,50,50,buffer,strlen(buffer));
					return 0;
				}
				break;
			case WA_CLICKACTIVE:
				{
					sprintf(buffer,"Window is Activated by Mouse");
					TextOut(hdc,50,50,buffer,strlen(buffer));
					return 0;
				}
				break;
			case WA_INACTIVE:
				{
					sprintf(buffer,"Window is Deactivated");
					TextOut(hdc,50,50,buffer,strlen(buffer));
					return 0;
				}
				break;
			}
			return 0;
		}
		break;
	case WM_COMMAND:
		{
			switch(wparam)
			{
			case ID_FILES_EXIT:
				{
					PostQuitMessage(0);
					return 0;
				}
			case ID_FILES_CLOSE:
				{
					PostMessage(hwnd,WM_DESTROY,wparam,lparam);
					return 0;
				}
				break;
			case ID_WINDOW_REPAINT:
				{
					PostMessage(hwnd,WM_PAINT,0,0);
					return 0;
				}
				break;
			}
			return 0;
		}
		break;
	case WM_CLOSE:
		{
			int Answer=0;
			Answer=MessageBox(hwnd,"Are You Sure??","Sure??",MB_YESNO);
			if(Answer==IDYES)
			{
				SendMessage(hwnd,WM_DESTROY,wparam,lparam);
			}
			return 0;
		}
		break;
	case WM_DESTROY:
		{

			--WindowCounter;
			if(WindowCounter<=0)
			{
				PostMessage(hwnd,WM_QUIT,wparam,lparam);
			}
			return 0;
		}
		break;
	}
	return (DefWindowProc(hwnd,msg,wparam,lparam));
}


/////////////////////////////////WINPROC////////////////////////////////////////////////////


int WINAPI WinMain(HINSTANCE hInstance,HINSTANCE hPrevInstance,LPSTR lpCmdLine,int nShowCmd)
{
	srand(time(NULL));
	SparehInstance=hInstance;
	WNDCLASSEX myclass;
	MSG msg;
	HWND hwnd;
	myclass.cbClsExtra=0;
	myclass.cbSize=sizeof(WNDCLASSEX);
	myclass.cbWndExtra=0;
	myclass.hbrBackground=(HBRUSH) GetStockObject(WHITE_BRUSH);
	myclass.hCursor=LoadCursor(hInstance,MAKEINTRESOURCE(IDC_CURSOR1));
	myclass.hIcon=LoadIcon(hInstance,MAKEINTRESOURCE(IDI_ICON1));
	myclass.hIconSm=LoadIcon(hInstance,MAKEINTRESOURCE(IDI_ICON1));
	myclass.hInstance=hInstance;
	myclass.lpfnWndProc=WinProc;
	myclass.lpszClassName=CLASSNAME;
	myclass.lpszMenuName=NULL;
	myclass.style=CS_HREDRAW|CS_VREDRAW|CS_OWNDC|CS_DBLCLKS;
	if(!(RegisterClassEx(&myclass)))
	{
		MessageBox(NULL,"Registration Error","Reg.Err",MB_OK);
		return 0;
	}
	if(!(hwnd=CreateWindowEx(NULL,CLASSNAME,WINDOWCAPTION,WS_OVERLAPPEDWINDOW|WS_VSCROLL,
		CW_USEDEFAULT,CW_USEDEFAULT,CW_USEDEFAULT,CW_USEDEFAULT,NULL,NULL,hInstance,NULL)))
	{
		MessageBox(NULL,"Creation Error","Crt.Err.",MB_OK);
		return 0;
	}
	SetMenu(hwnd,LoadMenu(hInstance,MAKEINTRESOURCE(IDR_MENU1)));
	ShowWindow(hwnd,SW_MAXIMIZE);
	UpdateWindow(hwnd);
	while(true)
	{
		if(PeekMessage(&msg,hwnd,0,0,PM_REMOVE))
		{
			if(msg.message==WM_QUIT)
			{
				break;
			}
			TranslateMessage(&msg);
			DispatchMessage(&msg);
		}
	}
	return (msg.wParam);
}

You need to use the InvalideRect command. This is very useful as you only need to redraw the area of the screen which has changed. The syntax is InvalidateRect(HWND, *RECT, bool). The first is obviously your window, the second is a pointer to a RECT structure which is the area you want to invalidate and the bool states whether or not you want to clear the previous area before redraw.

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