code:

/* hello.c -- initialize the toolkit using an application context 
** and a toplevel shell widget, then create a pushbutton that says
** Hello using the varargs interface. 
*/

#include <Xm/PushB.h>

main (int argc, char *argv[])
{
    Widget           toplevel, button;
    XtAppContext     app;
    void             button_pushed(Widget, XtPointer, XtPointer);
    XmString         label;
    Arg              args[2];

    XtSetLanguageProc (NULL, NULL, NULL);
    toplevel = XtVaOpenApplication (&app, "Hello", NULL, 0, &argc, argv,
                                    NULL,sessionShellWidgetClass, NULL);    
    label = XmStringCreateLocalized ("Push here to say hello");
    XtSetArg(args[0], XmNlabelString, label);
    button = XmCreatePushButton (toplevel, "pushme", args, 1);
    XmStringFree (label);
    XtAddCallback (button, XmNactivateCallback, button_pushed, NULL);
    XtManageChild (button);
    XtRealizeWidget (toplevel);
    XtAppMainLoop (app);
}

void button_pushed (Widget widget, XtPointer client_data, XtPointer call_data)
{
    printf ("Hello Yourself!\n");
}