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# ECE-203 Homework Week 3 solution

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ECE-203 Programming for Engineers
Homework Week 3

(50 Points) The last digit of a credit card number is the check digit, which protects against
transcription errors such as an error in a single digit or the transposition of two adjacent digits. The
following method is used to verify actual credit card numbers but (for simplicity) we will describe
it for a number with 8 digits instead of 16.
• Starting form the rightmost digit, form the sum of every other digit.
– Example: if the card number is 4358 9795, then you form the sum: 5 + 7 + 8 + 3 = 23
• Double each of the digits that were not included in the previous step. Add all the digits of
the resulting numbers.

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ECE-203 Programming for Engineers
Homework Week 3

(50 Points) The last digit of a credit card number is the check digit, which protects against
transcription errors such as an error in a single digit or the transposition of two adjacent digits. The
following method is used to verify actual credit card numbers but (for simplicity) we will describe
it for a number with 8 digits instead of 16.
• Starting form the rightmost digit, form the sum of every other digit.
– Example: if the card number is 4358 9795, then you form the sum: 5 + 7 + 8 + 3 = 23
• Double each of the digits that were not included in the previous step. Add all the digits of
the resulting numbers.
– Example: for the card number 4358 9795, the not included digits were [9, 9, 5, 4]. Doubling these leads to [18, 18, 10, 8]. Summing the digits results in:
1 + 8 + 1 + 8 + 1 + 0 + 8 = 27
• Add the sums from the previous two steps. If the last digit of the sum is zero, then the credit
card number is valid.
– Example: for the number 4358 9795, this step gives 23 + 27 = 50. The last digit of 0
means the number is valid.
Write a program that accepts a number from the user via a prompt and perform the above algorithm
to check if the number is valid or not. If the number is valid, print a message to the screen informing
the user. Your program should be capable of performing the algorithm on a number consisting of
any number of digits.
(Hint: When isolating individual digits, it is useful work on the number as a string, which is just
a sequence of characters. When performing arithmetic, you will need to convert characters into
integers. Remember, the function int() is used to convert floats or strings containing number
characters into integers. Likewise, the function str() is used to convert ints or floats into a string
of number characters.)
The output of your program should display the credit card number entered and its validity status.
For example:
43589795 is a VALID credit card number.
Test your program with the following numbers (spaced provided simply to make reading easier, your
program does not need to handle spaces.):
4358 9795
5979 8534 3339 4390
4561 3256 2991 3234
2349 1291 2347
3219 3231 3999
4092 6117 5811 4081
7591 7413 3009 6174 6711 9469 0997 4528
3432 1112 3223 0921
(Hint: Using just what has been covered so far in lecture, this can be accomplished in as little as 14
lines of code.)
1
Name your program ccverify.py and save its output as ccverify.txt. The output should show
your interaction with the program testing the 8 provided test numbers. The easiest way to save this
output is to simply highlight, copy, and paste into a plaintext file.