Проблема с запуском окна

#include "windows.h"
LRESULT CALLBACK WndProc(HWND hWnd, UINT mes, WPARAM wParam, LPARAM lParam);
WNDCLASS wc = { 0, WndProc, 0, 0, 0, 0, 0,(HBRUSH)(COLOR_WINDOW + 1), L"class" };
MSG msg;
HWND hMainWnd;
int __stdcall WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, char*CmdLine, int ShowCmd)
{
    wc.hCursor = LoadCursor(0, IDC_ARROW);
    wc.hIcon = LoadIcon(0, IDI_APPLICATION);
    wc.hInstance = hInstance;
    RegisterClass(&wc);
    hMainWnd = CreateWindowEx(WS_EX_CLIENTEDGE, L"class", L"Курсовая работа", WS_SYSMENU, 300, 300, 500, 500, 0, 0, wc.hInstance, 0);
    ShowWindow(hMainWnd, 3);
    while (GetMessage(&msg, 0, 0, 0) != 0)
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
}
 
LRESULT WndProc(HWND hWnd, UINT mes, WPARAM wParam, LPARAM lParam)
{
    switch (mes)
    {
    case WM_CREATE:
        CreateWindowEx(0, L"BUTTON", L"BUTTON", WS_CHILD | WS_VISIBLE, 10, 45, 75, 25, hWnd, 0, wc.hInstance, 0);
        return 0;
    case WM_DESTROY:
    {
        PostQuitMessage(0);
        return 0;
        break;
    }
    default: return DefWindowProc(hWnd, mes, wParam, lParam);
    }
}

WNDCLASS wc = { 0, WndProc, 0, 0, 0, 0, 0,(HBRUSH)(COLOR_WINDOW + 1), 0, L"class" };