Create a single program that contains a main function, and one additional function per problem, that is,
a total of five functions plus main. Provide a sample run.
1. Write a function that will return the sum of the digits of a natural number $n$, where $n > 0$.
2. Modify the above function and come up with a new function that will return the sum of the squares
of the digits of $n$.
3. Also come up with a function that will count and return the number even digits of $n$.
4. Write a function that will find the maximum value of the digit in a given multi-digit number $n > 0$.
5. Modify the above function to return the minimum value instead.
