While loop comparing two variables

Question

I'm trying to find and print the minimum value for n that satisfies ca >= cb:

ap = 80000
bp = 200000
at = 1.03
bt = 1.015
n = 1
ca = ap*at*n
cb = bp*bt*n

while cb > ca:
    n = n + 1
    print(n)

The code just runs and prints n + 1 indefinitely, though. What is the correct approach to this problem?

The assignments to ca and cb were one-time events. They don't auto-update in response to later changes to n, which seems to be what you were expecting to happen. You need to recalculate them each time through the loop — jasonharper
– jasonharper, Commented Sep 20, 2017 at 5:36
Put the actual question you had in hand. Your logic is not correct. — Amit Kumar Singh
– Amit Kumar Singh, Commented Sep 20, 2017 at 7:39

ksha · Accepted Answer · 2017-09-20 05:44:47Z

1

ap = 80000
bp = 200000
at = 1.03
bt = 1.015
n = 1
ca = ap*at*n
cb = bp*bt*n

while cb > ca:
  n += 1
  ca = ap*at*n
  cb = bp*bt*n

This won't converge though.

answered Sep 20, 2017 at 5:41

ksha

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4 Comments

this doesn't converge: as long as bp*bt is greater than ap*at, the change of n won't change the truth of cb > ca

this code may come to an end if you use finite data types, like in c, but not in python

Correct @Aemyl I was just editing my answer for that :)

thanks ketan! your answer and a little change in my logic solved my problem