Question

a simple algorithm to reverse the digits of a number

Answer 1

in which language.

Answer 2

The trick to this type of problem is to convert the number into a character string.

A string is a collection of characters, so you can iterate over the collection and assemble (concatenate) a new string.

Answer 3

And if the result needs to be a number, you can do the string back to a number after.

Another way is to use % to get the remainders and strip off the last didgets one by one and add to a new number that you multiply by 10 as you go through each, and subtract off what you find so when the original is 0 you know you are done.