How to use user input to end a program?

Question

I'm new to python and I am writing a program that converts Millimeters to Inches. Basically its a continuous loop that allows you to keep putting in numbers and get the correct converted measurement. I want to put an IF statement that will allow the user to type "end" to end the program instead of converting more units of measurement. How would I go about making this work (what python code allows you to exit a written program and can be used in an IF statement.)?

convert=float(25.4)
while True:
    print("*******MM*******")
    MM=float(input())
    Results=float(MM/convert)
    print("*****Inches*****")
    print("%.3f" % Results)
    print("%.4f" % Results)
    print("%.5f" % Results)

Answer 1

To end the loop, you can use a break statement. This can be used inside an if statement, since break only looks at loops, not conditionals. So:

if user_input == "end":
    break

Notice how I used user_input, not MM? That's because your code has a minor problem right now: you're calling float() before you ever check what the user typed. Which means if they type "end", you'll call float("end") and get an exception. Change your code to something like this:

user_input = input()
if user_input == "end":
    break
MM = float(user_input)
# Do your calculations and print your results

One more improvement you can make: if you want the user to be able to type "END" or "End" or "end", you can use the lower() method to convert the input to lowercase before comparing it:

user_input = input()
if user_input.lower() == "end":
    break
MM = float(user_input)
# Do your calculations and print your results

Make all those changes, and your program will work the way you want it to.