Почему возникают ошибки в этом примере??

// Proj.cpp : Defines the entry point for the application.
//
 
 
#include "stdafx.h"
#include "windows.h"
#include "windowsx.h"
 
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM,LPARAM);
 
int APIENTRY WinMain(
        HINSTANCE hInstance,
        HINSTANCE hPrevInstance,
        LPSTR lpCmdLine,
        int nCmdShow)
{
    HWND hwnd;
    MSG msg;
    WNDCLASS w;
    char szClassName[]="Hello World";
    memset(&w,0,sizeof(WNDCLASS));
    w.style = CS_HREDRAW | CS_VREDRAW;
    w.lpfnWndProc = WndProc;
    w.cbClsExtra = 0;
    w.cbWndExtra = 0;
    w.hInstance = hInstance;
    w.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    w.hCursor = LoadCursor(NULL, IDC_ARROW);
    w.hbrBackground = (HBRUSH) GetStockObject(WHITE_BRUSH);
    w.lpszMenuName = NULL;
    w.lpszClassName = szClassName;
    RegisterClass(&w);
    hwnd = CreateWindow("C Windows","C Windows", WS_OVERLAPPEDWINDOW,
        10,10,600,480,NULL,NULL,hInstance,NULL);
    ShowWindow(hwnd,nCmdShow);
    UpdateWindow(hwnd);
    while(GetMessage(&msg,NULL,0,0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    return msg.wParam;
}
 
LRESULT CALLBACK WndProc(HWND hWnd, UINT Message, WPARAM wparam,LPARAM lparam)
{
    HDC hDC;
    PAINTSTRUCT PaintStruct;
    RECT Rect;
    switch (Message)
    {case WM_PAINT:
        hDC = BeginPaint(hWnd, &PaintStruct);
        GetClientRect(hWnd,&Rect);
        DrawText(hDC, "Hello world!", -1, &Rect, DT_SINGLELINE|DT_CENTER|DT_VCENTER);
        EndPaint(hWnd, &PaintStruct);
        return 0;
     case WM_DESTROY:
        PostQuitMessage(0);
        return 0;
    }
    return DefWindowProc(hWnd,Message,wparam,lparam);
}

#define  UNICODE
#define _UNICODE
 
#include <windows.h>
#include <tchar.h>
 
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
 
INT WINAPI _tWinMain(HINSTANCE hInst, HINSTANCE, PTSTR pszCmd, INT iSc)
{
    MSG msg;
    HWND hWnd;
    WNDCLASSEX wnd;
 
    wnd.cbSize      = sizeof(wnd);
    wnd.cbClsExtra      = NULL;
    wnd.cbWndExtra      = NULL;
    wnd.hbrBackground   = (HBRUSH)GetStockObject(WHITE_BRUSH);
    wnd.hCursor     = LoadCursor(NULL, IDC_ARROW);
    wnd.hIcon       = LoadIcon(NULL, IDI_WINLOGO);
    wnd.hIconSm     = LoadIcon(NULL, IDI_WINLOGO);
    wnd.hInstance       = hInst;
    wnd.lpfnWndProc     = WndProc;
    wnd.lpszClassName   = _T("My_class_name");
    wnd.lpszMenuName    = NULL;
    wnd.style       = CS_HREDRAW | CS_VREDRAW;
 
    if(!RegisterClassEx(&wnd))
    {
        // Error ...
        // MessageBox(NULL, _T("ERROR #1"), _T("Error"), MB_ICONSTOP | MB_OK);
        return FALSE;
    }
 
    hWnd = CreateWindowEx(NULL, _T("My_class_name"), _T("WinAPI Programme"), WS_OVERLAPPEDWINDOW, 200, 200, 500, 300, 0, 0, hInst, 0);
 
    if(!hWnd)
    {
        // Error ...
        // MessageBox(NULL, _T("ERROR #2"), _T("Error"), MB_ICONSTOP | MB_OK);
        return FALSE;
    }
 
    ShowWindow(hWnd, iSc);
 
    while(GetMessage(&msg, NULL, NULL, NULL))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
 
    return msg.wParam;
}
 
LRESULT CALLBACK WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    HDC hDC;
    PAINTSTRUCT ps;
    static RECT rect;
 
    switch(uMsg)
    {
    case WM_PAINT:
        hDC = BeginPaint(hWnd, &ps);
        DrawText(hDC, _T("Hello Win32 world ! :)"), -1, &rect, DT_SINGLELINE | DT_CENTER | DT_VCENTER);
        EndPaint(hWnd, &ps);    
        break;
 
    case WM_SIZE:
        GetClientRect(hWnd, &rect);
        break;
 
    case WM_CLOSE:
        DestroyWindow(hWnd);
        break;
 
    case WM_DESTROY:
        PostQuitMessage(NULL);
        break;
 
    default:
        return DefWindowProc(hWnd, uMsg, wParam, lParam);
    }
 
    return FALSE;
}

        hwnd = CreateWindow( szClassName,"C Windows", WS_OVERLAPPEDWINDOW,
                10,10,600,480,NULL,NULL,hInstance,NULL);
        if ( !hwnd ) { 
            MessageBox(  NULL, "CreateWindow : error ", "Error", MB_OK|MB_ICONERROR); 
            return 1; 
        }