Insert a program inside a windows.h window in C

I have this code in C using the windows.h library for creating a simple window. How to implement a program so that it appears within this window.

#include <windows.h>

const char g_szClassName[] = "ClassedaJanela";

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
switch(msg)
{
    case WM_CLOSE:
        DestroyWindow(hwnd);
    break;
    case WM_DESTROY:
        PostQuitMessage(0);
    break;
    default:
        return DefWindowProc(hwnd, msg, wParam, lParam);
}
return 0;
}

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
LPSTR lpCmdLine, int nCmdShow)
{
WNDCLASSEX wc;
HWND hwnd;
MSG Msg;

wc.cbSize        = sizeof(WNDCLASSEX);
wc.style         = 0;
wc.lpfnWndProc   = WndProc;
wc.cbClsExtra    = 0;
wc.cbWndExtra    = 0;
wc.hInstance     = hInstance;
wc.hIcon         = LoadIcon(NULL, IDI_APPLICATION);
wc.hCursor       = LoadCursor(NULL, IDC_ARROW);
wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
wc.lpszMenuName  = NULL;
wc.lpszClassName = g_szClassName;
wc.hIconSm       = LoadIcon(NULL, IDI_APPLICATION);

if(!RegisterClassEx(&wc))
{
    MessageBox(NULL, "Window Registration Failed!", "Error!",
        MB_ICONEXCLAMATION | MB_OK);
    return 0;
}

hwnd = CreateWindowEx(
    WS_EX_CLIENTEDGE,
    g_szClassName,
    "Simple Window",
    WS_OVERLAPPEDWINDOW,
    CW_USEDEFAULT, CW_USEDEFAULT, 240, 120,
    NULL, NULL, hInstance, NULL);

if(hwnd == NULL)
{
    MessageBox(NULL, "Window Creation Failed!", "Error!",
        MB_ICONEXCLAMATION | MB_OK);
    return 0;
}

ShowWindow(hwnd, nCmdShow);
UpdateWindow(hwnd);

// Step 3: The Message Loop
while(GetMessage(&Msg, NULL, 0, 0) > 0)
{
    TranslateMessage(&Msg);
    DispatchMessage(&Msg);
}
return Msg.wParam;
}