Can someone explain to me why doesn't this piece of code work?

Question

annual_salary = int(input("Your annual salary "))
semi_annual_raise = 0.07
r = 0.04
down_payment = 250000
epsilon = 100
low = 0
high = 10000
guess = (high + low)//2
best_saving_rate = (guess/10000)
months = 0
current_savings = 0
steps = 0

while abs(current_savings - down_payment) >= 100:
    for i in range(36):
        current_savings += best_saving_rate*(annual_salary/12) + (current_savings*r)/12
        months +=1
        if months%6 == 0:
            annual_salary = annual_salary + semi_annual_raise*annual_salary  
    if current_savings < down_payment:
        low = guess
    else:
        high = guess
    steps += 1
    guess = (high + low)//2
    best_saving_rate = float(guess/10000)
print(steps)
print(best_saving_rate)
print(current_savings)

This code is supposed to find the best saving rate for someone who is trying to have enough money for a payment of 250000 dollars in 36 months. I use bisection search and I think I'm in the right track but it won't work. I think the problem is that the variable current savings is not reinitializing with every iteration and I do not know how to make it do that. PLEASE HELP.

What happens on every iteration is determined by the indented lines following the line that starts with `while`. If you want something more to happen on every iteration, perhaps you should add an indented line to this block. — Dennis Sparrow, Jul 14 '20 at 02:09
The reason that I think that the code is not working is because "current_savings" is not reseting to 0 with every iteration. So with the end of the first iteration with a salary of 150k it outputs 283387.2k, but the second output of the second iteration is 532098.3k. So it seems to be saving the value of the iteration before when it should be resting itself to 0 and starting the second iteration with that value(0). BTW this is an assignment from MIT for students in 6,0001. — bassam ch, Jul 14 '20 at 03:22
If you think current_savings needs to be set to 0 again, why don't you do so? — MisterMiyagi, Jul 14 '20 at 05:41

Glenn Mackintosh · Accepted Answer · 2020-07-14T04:00:14.047

0

Why are you expecting the current_savings to be reset to 0 with every iteration? You do not do that in the code, so what would cause that to happen? Also by the looks of the code, you should be resetting months to 0 as well (though it appears that the for loop index variable i should actually be the month).

This fixes the obvious errors that I could see:

while abs(current_savings - down_payment) >= 100:
    current_savings = 0   # add this
    for month in range(36):  # Change this
        current_savings += best_saving_rate * (annual_salary / 12) + (current_savings * r) / 12
        # months += 1  <-- remove this
        if months % 6 == 0:

edited Jul 14 '20 at 04:00

answered Jul 14 '20 at 03:53

Glenn Mackintosh

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Thanks, you're right all I had to do was, like you pointed out, rewrite the variables at the beginning of the while loop. Although the months part changes a bit the output I expected. – bassam ch Jul 14 '20 at 05:49

Can someone explain to me why doesn't this piece of code work?

1 Answers1