int scancode_to_ascii(int scancode);
Converts the given scancode to an ASCII character for that key (mangling Unicode values), returning the unshifted uncapslocked result of pressing the key, or zero if the key isn't a character-generating key or the lookup can't be done. The lookup cannot be done for keys like the F1-F12 keys or the cursor keys, and some drivers will only return approximate values. Generally, if you want to display the name of a key to the user, you should use the scancode_to_name function.
int ascii; ... ascii = scancode_to_ascii(scancode); allegro_message("You pressed '%c'\n", ascii);