[Solved] ISSN Calculator in Python

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IMMEDIATE PROBLEM

You increment your index value before you use it; this means that on the final iteration, it’s 1 too large for the final operation. Switch the bottom two lines of your loop:

index = 0 
while index < 7: 
    print(arr[index])
    totalNum = int(num[index]) * arr[index]
    index += 1

Even better, this should be a for loop, not a while:

for index in range(7):
    print(arr[index])
    totalNum = int(num[index]) * arr[index]

Python will guard your value better.

AFTER THIS REPAIR:

8
7
6
5
4
3
2
14
['0317847', -8]

Now, your problems include

  • You keep only the last weighted amount in totalNum. You need to make a running sum for the entire group.
  • You have the final subtraction backwards.

I assume you can fix things from here.
Remember that you still have to handle the X case.

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solved ISSN Calculator in Python