set_hardware_volume - Alters the hardware sound output volume. Allegro game programming library.

       Alters  the  hardware sound output volume. Specify volumes for both digital samples and MIDI playback, as
       integers from 0 to 255, or pass a negative value to leave one of the settings  unchanged.  Values  bigger
       than  255  will  be  reduced to 255. This routine will use the hardware mixer to control the volume if it
       exists (i.e. the volume of all the applications on your machine will be affected), otherwise do nothing.

       set_hardware_volume - Alters the hardware sound output volume. Allegro game programming library.

install_sound(3alleg4), set_volume(3alleg4)

Allegro                                           version 4.4.3                     set_hardware_volume(3alleg4)

#include<allegro.h>voidset_hardware_volume(intdigi_volume,intmidi_volume);