#include <windows.h>
#include <time.h>
LRESULT CALLBACK WndProc(HWND,UINT,WPARAM,LPARAM);
HINSTANCE g_hInst;
LPSTR lpszClass="MyTimer";

int count1=0;
int count2=0;

int APIENTRY WinMain(HINSTANCE hInstance,HINSTANCE hPrevInstance
    ,LPSTR lpszCmdParam,int nCmdShow)
{
 HWND hWnd;
 MSG Message;
 WNDCLASS WndClass;
 g_hInst=hInstance;
 
 WndClass.cbClsExtra=0;
 WndClass.cbWndExtra=0;
 WndClass.hbrBackground=(HBRUSH)GetStockObject(WHITE_BRUSH);
 WndClass.hCursor=LoadCursor(NULL,IDC_ARROW);
 WndClass.hIcon=LoadIcon(NULL,IDI_APPLICATION);
 WndClass.hInstance=hInstance;
 WndClass.lpfnWndProc=(WNDPROC)WndProc;
 WndClass.lpszClassName=lpszClass;
 WndClass.lpszMenuName=NULL;
 WndClass.style=CS_HREDRAW | CS_VREDRAW;
 RegisterClass(&WndClass);

 hWnd=CreateWindow(lpszClass,lpszClass,WS_OVERLAPPEDWINDOW,
    CW_USEDEFAULT,CW_USEDEFAULT,CW_USEDEFAULT,CW_USEDEFAULT,
    NULL,(HMENU)NULL,hInstance,NULL);
 ShowWindow(hWnd,nCmdShow);
 
 while(GetMessage(&Message,0,0,0)) {
  TranslateMessage(&Message);
  DispatchMessage(&Message);
 }
 return Message.wParam;
}

LRESULT CALLBACK WndProc(HWND hWnd,UINT iMessage,WPARAM wParam,LPARAM lParam)
{
 HDC hdc;
 PAINTSTRUCT ps;
 static HANDLE hTimer;
 SYSTEMTIME st;
 static char sTime1[128];
 static RECT rt1;
 static RECT rt2;
 static RECT rt3; 
 int str1 = 0;
 int str2 = 0;
 static SIZE size1,size2;

 srand(time(NULL));

 switch(iMessage) {
 case WM_CREATE:
  hdc = GetDC (hWnd) ;
  ReleaseDC (hWnd, hdc) ;
    
  hTimer=(HANDLE)SetTimer(hWnd,1,500,NULL);
  SendMessage(hWnd, WM_TIMER, 1, 0);
  
  return 0;
 case WM_TIMER:
  GetLocalTime(&st);
  hdc = GetDC (hWnd) ;
  
  wsprintf(sTime1,"%d + %d = ?",rand()%31,rand()%31);
  
  GetTextExtentPoint(hdc, sTime1, strlen(sTime1), &size1);
  if(count1 ==0)
  { 
   str1 = size1.cx;
   count1++;
  }
  
  else
  {
   str2 = size1.cx;
  }
  GetClientRect(hWnd,&rt2);
  rt2.right = rt2.right/2;
  rt2.bottom = rt2.bottom/2;
  if(str1 >= size1.cx)
  {
   rt1.right = rt2.right + str1/2;
   rt1.left = rt2.right- str1/2;
   rt1.top = rt2.bottom - size1.cy/2;
   rt1.bottom = rt2.bottom + size1.cy/2;

  }
  else if(str1 < str2)
  {
   str1 = str2;
   rt1.right = rt2.right + str2/2;
   rt1.left = rt2.right- str2/2;
   rt1.top = rt2.bottom - size1.cy/2;
   rt1.bottom = rt2.bottom + size1.cy/2;
   
  }
  
  InvalidateRect(hWnd,&rt1,TRUE);
  return 0;
 
 case WM_PAINT:
  hdc=BeginPaint(hWnd,&ps);
    
  TextOut(hdc,rt2.right-size1.cx/2,rt2.bottom-size1.cy/2,sTime1,strlen(sTime1));

  EndPaint(hWnd,&ps);
  return 0;

 case WM_DESTROY:
  KillTimer(hWnd,1);
  PostQuitMessage(0);
  return 0;
 }
 return(DefWindowProc(hWnd,iMessage,wParam,lParam));
}

이게  GetClientRect사용해서 가운데 정렬시키고
문자열길이만큼 무효영역 설정해주고 출력하는건데
아무리생각해도 어디가 틀린건지 모르겠어욤
조언부탁드립니다.