A “sentinel value” in a program is a value that indicates the end of a series. In a loop, when the sentinel value is reached, the loop finishes repeating.
Write a program sentinel_hello.py that asks people to enter their name. Every time a name is entered the program prints a personalized “Hello” greeting using their name. If the user hits [Enter] without entering a name, however–a sentinel value of “” (the “empty string”)–the program says “Goodbye” and ends.