CODEWITHSUNDEEP
pythonpython-3.xinfinite-loop
gab
gab

Reputation: 21

Why do I have an infinite loop in my code?

Below I have a piece of code which calculates credit card balance, but it doesn't work when balance has an extreme value (such as balance=9999999999below). It throws the code through an infinite loop. I have a couple of theories as to how to fix this flaw, but don't know how to move forward with them. Here's my code:

balance = 9999999999
annualInterestRate = 0.2
monthlyPayment = 0

monthlyInterestRate = annualInterestRate /12
newbalance = balance
month = 0

while newbalance > 0:
    monthlyPayment += .1
    newbalance = balance

    for month in range(1,13):
        newbalance -= monthlyPayment
        newbalance += monthlyInterestRate * newbalance
        month += 1
print("Lowest Payment:" + str(round(monthlyPayment,2)))

My theory is that while newbalance > 0 is causing the infinite loop, because newbalance is always larger than 0.

How can I change this while loop so that it doesn't cause my code to run infinitely?

By the way: With moderate numbers, the program runs for a long time and finally gives an answer. For the larger numbers, the program just keeps on going.

Upvotes: 1

Views: 169

Answers (2)

BWhite
BWhite

Reputation: 46

The bisection method will execute much quicker if you're allowed to use it in your assignment. Will not help you though, if you're required to increment the monthly payment by .01.

static_balance = balance
interest = (annualInterestRate/12)
epsilon = 0.01
lo = balance/12
hi = balance

while abs(balance) > epsilon:
    balance = static_balance
    min_pmt = (hi+lo)/2
    for i in range(12):
        balance -= min_pmt
        balance *= 1+interest
    if balance > 0:
        lo = min_pmt
    else:
        hi = min_pmt
print("Lowest payment: ", round(min_pmt, 2))

Upvotes: 0

Patrick Haugh
Patrick Haugh

Reputation: 60994

This loop is not infinite, but will take a long time to resolve. For very large values of balance, monthlyPayment will have to get very large in order to drop it past zero.

Upvotes: 3

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