求解决，编译通过了，为啥不有窗口，谢谢！

求解决，编译通过了，为啥不有窗口，谢谢！
#include <windows.h>
#include<stdio.h>
LRESULT CALLBACK WndProc(HWND hwnd,UINT uMsg,WPARAM wParam,LPARAM lParam);
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,LPSTR lpCmdLine, int nCmdShow)
{   HWND hwnd;
    WNDCLASS wndcls;
    MSG msg;
    UNREFERENCED_PARAMETER(lpCmdLine);
    wndcls.style=CS_HREDRAW|CS_VREDRAW;
    wndcls.lpszMenuName=NULL;
    wndcls.lpszClassName="ex1";
    wndcls.cbClsExtra=0;
    wndcls.cbWndExtra=0;
    wndcls.lpfnWndProc=WndProc;
    wndcls.hIcon=LoadIcon(NULL,IDI_ERROR);
    wndcls.hbrBackground=(HBRUSH)GetStockObject(BLACK_BRUSH);
    wndcls.hCursor=LoadCursor(NULL,IDC_CROSS);
    wndcls.hInstance=hInstance;
    RegisterClass(&wndcls);
    hwnd=CreateWindow("ex1","第一个Windows程序",WS_OVERLAPPEDWINDOW,0,0,600,400,NULL,NULL,hInstance,NULL);
    ShowWindow(hwnd,SW_SHOWNORMAL);
    UpdateWindow(hwnd);

    while(GetMessage(&msg,NULL,0,0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
        
        }
    return 0/*(msg.wParam)*/;//原文是返回0;
}
LRESULT CALLBACK WndProc( HWND hwnd,  UINT uMsg,WPARAM wParam, LPARAM lParam)
{
    char *szChar="\0";   
    switch(uMsg)
    {
    case WM_CLOSE:
        if(IDYES==MessageBox(hwnd, "是否真的结束？ ",
                "确认结束程序",MB_YESNO))
            DestroyWindow(hwnd);
        break;
    case WM_DESTROY:
        PostQuitMessage(0);   
        break;
    case WM_CHAR:
        
        sprintf(szChar, "你按下了%c",wParam);
        MessageBox(hwnd,szChar, "字符",0);  
        break;
    case WM_LBUTTONDOWN:
        MessageBox(hwnd, "你单击了鼠标左键","鼠标单击通知",0);
        break;
    default:
        return DefWindowProc(hwnd,uMsg,wParam,lParam);
    }
    return 0;
}