number of digits in integer number using prolog

Question

can someone help me with this problem ?

numofdig(A,B):-
   A>0,
   A is (A//10),
   succ(0,S),
   numofdig(A),
   B is S,
   write(B).

this is my code and its not working .

Answer 1

I'd do this:

number_of_digits( M , N ) :-
  integer(M),              % is it an integer?
  V is abs(M),             % sign is irrelevant as to number of digits
  number_of_digits(V,1,N). % invoke the helper predicate with the accumulator seeded with 1 (all numbers have at least one digit).

number_of_digits( M , T , N ) :-
    M > 9,                        % Is the value > 9?
    !,                            %   If so, eliminate the choice point (it's not going to stop being 10+ on backtracking)
    T1 is T+1 ,                   %   Increment the accumulator
    M1 is M // 10 ,               %   drop the rightmost digit via integer division by 10
    number_of_digits(M1,T1,N)     %   and recurse down on what's left.
    .                             % Otherwise (the value is 0-9)
number_of_digits( _ , N , N ) .   %   The accumulator has the result.