CODEWITHSUNDEEP
pythonloopsfor-loopequation
user1855147
user1855147

Reputation: 9

Python for loop with adding to an equation?

I need some help in this program. I need help figuring out how to make it calculate interest for a period over ten years (including the first one). This is as far as i have gotten on my own. I would greatly appreciate some insight to this problem.

Thanks. *The "print() is just for spacing so that the program looks cleaner.

p= int(input(" Intial Amount? "))
print()
r= float(input(" Rate? (Decimal) "))
print()
n= int(input(" Number Of Times Compunded? (Yearly) "))
print()
t= float(input(" Number Of Years? "))
A= p*(1+r/n)**(n*t)
print()
print( " Interest At Final Year","$",format(A, ',.2f'))
print()
for i in range (10):
    print(format(i+1, '3')," Year","Interest","$",format(A,',.2f'))

Upvotes: 0

Views: 10740

Answers (2)

mushroom
mushroom

Reputation: 6281

In the body of your loop, you are not updating the values of any of the variables. You need to update A at every iteration or store the intermediate results in some other variable. As an example, see the following:

def compound_interest(r, n, initial):
    current_value = initial
    for i in range(n):
        current_value *= (1 + r)
        print(current_value)

I use the current_value variable to save the intermediate results of the loop. If I had simply done initial * (1 + r) at every iteration then the value of initial would never change; the result of the calculation must be saved if you want to keep using it.

Upvotes: 3

abarnert
abarnert

Reputation: 366213

At the very end of the program it will count 1-10 but it will have the same amount as the first calculation.

Yes, that's because the only thing that happens in that loop is the print call. You're just calculating A all at once, before you get into the loop, and then using the same A over and over again.

I need help making it add the new values to add up while the "n" and the "p" are changing.

Well, you aren't changing n or p, and I don't think you need to. But you do need to change something. If you want to print a different value of A each time through the loop, you have to recalculate next year's A based on the previous year's A, or whatever else goes into determining the right value.

For example:

for year in range (10):
    jan1balance = p
    for period in range(n):
        p = p * (1 + r)
    print(format(year+1, '3')," Year","Interest","$",format(p - jan1balance,',.2f'))

Or:

for year in range (10):
    yearlyinterest = 0
    for period in range(n):
        periodinterest = p * r
        yearlyinterest += periodinterest
        p += periodinterest
    print(format(year+1, '3')," Year","Interest","$",format(yearlyinterest,',.2f'))

Upvotes: 0

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