#undef UNICODE
#include <windows.h>

int APIENTRY WinMain(HINSTANCE hInstance,
HINSTANCE hPrevInstance,
LPSTR lpCmdLine,
int nCmdShow)
{
char a[25] = "test";
MessageBox(NULL, LPCSTR(a) ,LPCSTR("WinAPI App"), 0); //сообщение
return 0;
}