Getting the number from the list of character codes

?- number_codes(N,[49, 50, 51]).  % the UCS-2 char codes for '1','2','3'
N = 123.

?- number_codes(N,[45, 50, 51]).  % 45 is the UCS-2 char code for '-'
N = -23.

?- number_codes(N,[43, 50, 51]).  % 43 is the UCS-2 char code for '+'
N = 23.

?- number_codes(N,[49, 50, 46, 49, 50]).
N = 12.12.

?- number_codes(N,[42, 50, 51]).  % 42 is the UCS-2 char code for '*': NOPE!
ERROR: Syntax error: Illegal number

A bit more readable: use 0'X notation, which results in the char code for character X:

?- number_codes(N,[0'+, 0'4, 0'5]).
N = 45.

Getting the list of character codes from a number

?- number_codes(-12,L).
L = [45, 49, 50].

?- number_codes(+12,L).
L = [49, 50].

?- number_codes(12.12,L).
L = [49, 50, 46, 49, 50].