Repetition Based on User Input

You can use function input in a loop to make the chemical formula translation example from , interactive. You will ask the user to enter a chemical formula, and your program, which is saved in a file named formulas.py, will print its name. The loop should continue until the user types quit:

​	text = ​""​
​	​while​ text != ​"quit"​:
​	text = input(​"Please enter a chemical formula (or 'quit' to exit): "​)
​	​if​ text == ​"quit"​:
​	​print​(​"…exiting program"​)
​	​elif​ text == ​"H2O"​:
​	​print​(​"Water"​)
​	​elif​ text == ​"NH3"​:
​	​print​(​"Ammonia"​)
​	​elif​ text == ​"CH4"​:
​	​print​(​"Methane"​)
​	​else​:
​	​print​(​"Unknown compound"​)

Since the loop condition checks the value of the text, you must assign it a value before the loop begins. Now, you can run the program in formulas.py, and it will exit whenever the user types quit:

​	Please enter a chemical formula (or 'quit' to exit): ​CH4​
​	Methane
​	Please enter a chemical formula (or 'quit' to exit): ​H2O​
​	Water
​	Please enter a chemical formula (or 'quit' to exit): ​quit​
​	…exiting program

The number of times that this loop executes will vary depending on user input, but it will iterate at least once.

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