I recently saw a Numberphile video about Kaprekar's constant. Kaprekar, an Indian mathematician defined a very simple yet very interesting iterative operation on a four digit number (with at least one distinct digit) which would always result in a constant (6174). It truly brings out the beauty in mathematics.
This app takes a four digit number input and goes through the intermediary steps to finally output the constant.
The most significant part of the project was figure out an implementation to keep track of the leading zeros. It was a fun little friday night coding project. The workings of the operation is described in the following picture.