set_volume - Alters the global sound output volume. Allegro game programming library.

       Alters  the  global  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 not alter the volume of the hardware mixer if it
       exists (i.e. only your application will be affected).

       set_volume - Alters the global sound output volume. Allegro game programming library.

install_sound(3alleg4), set_hardware_volume(3alleg4)

Allegro                                           version 4.4.3                              set_volume(3alleg4)

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