windows 程序设计自学:窗口正中显示Hello,World

#include <windows.h>

LRESULT CALLBACK MyWndProc(  HWND hwnd,      // handle to window
  UINT uMsg,      // message identifier
  WPARAM wParam,  // first message parameter
  LPARAM lParam   // second message parameter
  );

int WINAPI WinMain( HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nShowCmd )
{
    WNDCLASS wnd;
    HWND hwnd;
    MSG msg;
    wnd.style = CS_HREDRAW | CS_VREDRAW; //水平或垂直改变窗口都被重绘 与MyWndProc的WM_PAINT消息关联
    wnd.lpfnWndProc = MyWndProc;
    wnd.cbClsExtra = 0;
    wnd.cbWndExtra = 0;
    wnd.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wnd.hCursor = LoadCursor(NULL, IDC_ARROW);
    wnd.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
    wnd.lpszMenuName = NULL;
    wnd.lpszClassName = "HelloClass"; //窗口类标识,用在CreateWindow的第一个参数
    wnd.hInstance = hInstance;
    if(!RegisterClass(&wnd))
    {
        MessageBox(NULL, TEXT("无法创建窗口"), TEXT("ERROR"), MB_OK|MB_ICONERROR);
        return 0;
    }
    
    hwnd = CreateWindow("HelloClass", TEXT("Hello"), WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, NULL, NULL, hInstance, NULL); //第二个参数为窗口标题
    ShowWindow(hwnd, nShowCmd);
    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    return 0;
}

LRESULT CALLBACK MyWndProc(  HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    HDC hdc; //定义设备环境句柄
    PAINTSTRUCT ps; //绘制结构
    RECT rect; //矩形结构
    switch(uMsg)
    {
    case WM_PAINT:
    {    
        hdc = BeginPaint(hwnd, &ps);
        GetClientRect(hwnd, &rect);
        DrawText(hdc, TEXT("Hello,World!"), -1, &rect, DT_SINGLELINE|DT_CENTER|DT_VCENTER);
        EndPaint(hwnd, &ps);
    }
    break;    
    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;
    }

    return DefWindowProc(hwnd, uMsg, wParam, lParam);    
}