Split a number into a list of digits in Prolog

Question

I\'ve been having trouble trying to split numbers into lists using Prolog, e.g. 123456 becomes [1,2,3,4,5,6].

Can you please help me work out how to do

Answer 1

You could first create a reverse list:

//Base step
splitRev(0,[]).
//Recursive step
splitRev(N,[A|As]) :- N1 is floor(N/10), A is N mod 10, splitRev(N1,As).

The recursive step works like this:

N1 is floor(N/10)

divides N by 10 and rounds it down. So 538 becomes 53.8 becomes 53. It cuts off the last digit.

A is N mod 10

takes the remainder of N divided by 10. 538 mod 10 equals 8. So you get only the last digit.

Now for splitting the list you only need to reverse the list created by splitRev/2. So predicate split/2 is defined as:

split(N,L1) :- splitRev(N,L2), reverse(L1,L2).

Note that reverse/2 is a built-in predicate.

I hope this helps!