Is this character a digit? - part two

Write a program that reads a character from the keyboard and determines with the function is_digit from the previous exercise if it is one of the digits from 0 to 9. Write the program in such a way that it can be used to read several different characters from the keyboard until the user writes the word end.

An example of a test session you can execute manualy via the shell could be:

>>> %Run 
    Write a character or 'end' to finish: 4
    4 is a digit from 0 to 9
    Write a character or 'end' to finish: 56
    56 is not a digit from 0 to 9
    Write a character or 'end' to finish: z
    z is not a digit from 0 to 9
    Write a character or 'end' to finish: dfg
    dfg is not a digit from 0 to 9
    Write a character or 'end' to finish: 0
    0 is a digit from 0 to 9
    Write a character or 'end' to finish: end
>>>    

Insist that the students test their programs by giving them example
test runs.