Странное поведение

#include <windows.h>
LRESULT CALLBACK WndProc(HWND hwnd,UINT iMsg,WPARAM wParam,LPARAM lParam);
int WINAPI WinMain(HINSTANCE hInstance, 
    HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow)
{
    static wchar_t szAppName[]=L"Window";
    HWND hwnd;
    MSG msg;
    WNDCLASSEX wndclass;
 
    wndclass.cbSize=sizeof(wndclass);
    wndclass.style=CS_HREDRAW|CS_VREDRAW|CS_OWNDC;
    wndclass.lpfnWndProc=WndProc;
    wndclass.cbClsExtra=0;
    wndclass.cbWndExtra=0;
    wndclass.hInstance=hInstance;
    wndclass.hIcon=LoadIcon(NULL,IDI_APPLICATION);
    wndclass.hCursor=LoadCursor(NULL,IDC_ARROW);
    wndclass.hbrBackground=(HBRUSH)GetStockObject(WHITE_BRUSH);
    wndclass.lpszMenuName=NULL;
    wndclass.lpszClassName=szAppName;
    wndclass.hIconSm=LoadIcon(NULL,IDI_APPLICATION);
 
    RegisterClassEx(&wndclass);
 
    hwnd=CreateWindow(szAppName,L"Window",WS_MAXIMIZEBOX|WS_OVERLAPPEDWINDOW,CW_USEDEFAULT,
        CW_USEDEFAULT,CW_USEDEFAULT,CW_USEDEFAULT,NULL,NULL,hInstance,NULL);
    ShowWindow(hwnd,SW_SHOWMAXIMIZED);
    UpdateWindow(hwnd);
    while(BOOL lol=GetMessage(&msg,NULL,0,0))
    {   
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    return msg.wParam;
}
 
LRESULT CALLBACK WndProc(HWND hwnd,UINT iMsg,WPARAM wParam,LPARAM lParam)
{
    HDC hdc;
    PAINTSTRUCT ps;
    switch(iMsg)
    {
    case WM_CREATE:
        return 0;
    case WM_PAINT:
        {
            hdc=BeginPaint(hwnd,&ps);
            LineTo(hdc,rand()%500,rand()%500);
            EndPaint(hwnd,&ps);
            return 0;
        }
    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;
    }
    return DefWindowProc(hwnd,iMsg,wParam,lParam);
}