Integrating a for loop into an if statement

Question

This is kind of a double-barreled question, but it's got me puzzled. I currently have the following code:

from __future__ import division
import math

function = int(raw_input("Type function no.: "))


if function == 1:
    a = float(raw_input ("Enter average speed: "))
    b = float(raw_input ("Enter length of path: "))
    answer= float(b)/a
    print "Answer=", float(answer),

elif function == 2:
    mass_kg = int(input("What is your mass in kilograms?" ))
    mass_stone = mass_kg * 2.2 / 14
    print "You weigh", mass_stone, "stone."

else: print "Please enter a function number."

Now, I'd like to have some kind of loop (I'm guessing it's a for loop, but I'm not entirely sure) so that after a function has been completed, it'll return to the top, so the user can enter a new function number and do a different equation. How would I do this? I've been trying to think of ways for the past half hour, but nothing's come up.

Try to ignore any messiness in the code... It needs some cleaning up.

Answer 1

It's better to use a while-loop to control the repetition, rather than a for-loop. This way the users aren't limited to a fixed number of repeats, they can continue as long as they want. In order to quit, users enter a value <= 0.

from __future__ import division
import math

function = int(raw_input("Type function no.: "))

while function > 0:
    if function == 1:
        a = float(raw_input ("Enter average speed: "))
        b = float(raw_input ("Enter length of path: "))
        answer = b/a
        print "Answer=", float(answer),
    elif function == 2:
        mass_kg = int(input("What is your mass in kilograms?" ))
        mass_stone = mass_kg * 2.2 / 14
        print "You weigh", mass_stone, "stone."

    print 'Enter a value <= 0 for function number to quit.'
    function = int(raw_input("Type function no.: "))

You can tweak this (e.g., the termination condition) as needed. For instance you could specify that 0 be the only termination value etc.

An alternative is a loop that runs "forever", and break if a specific function number is provided (in this example 0). Here's a skeleton/sketch of this approach:

    function = int(raw_input("Type function no.: "))

    while True:
       if function == 1:
          ...
       elif function == 2:
          ...
       elif function == 0:
          break      # terminate the loop.

      print 'Enter 0 for function number to quit.'
      function = int(raw_input("Type function no.: "))

Note: A for-loop is most appropriate if you are iterating a known/fixed number of times, for instance over a sequence (like a list), or if you want to limit the repeats in some way. In order to give your users more flexibility a while-loop is a better approach here.