How I make program show dialog box and close?

I want make program...open up, it show dialog box, then close? Do nothing but show dialog. How Daler do that?

Code:

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#include <windows.h>

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
  MessageBox(NULL, "Hello", "test", MB_OK);
  return 0;
}

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Thank very much!