PHP Functions and Arrays

Overview

For this assignment you will implement a process to determine if an arbitrary account number is valid according to a series of calculations. When we create a new account number, we will add an extra digit at the end called the “check digit” as follows:

From the right-most digit, move left and double the value of every second digit. If the doubled number is greater than 9, then subtract 9 from the product. For example, if the doubled number is 14 we get 14 - 9 = 5. Observation: 14 - 9 = 5, but 1 + 4 = 5, so we can either subtract 9 or add the digits together.
Sum the digits of the resulting value in each position, call this value “s”.
The check digit is calculated as 10 - (s mod 10).

Example of calculating the check digit

Account number without check digit = 7992739871

In the following table “x” is a placeholder for the check digit we are about to calculate.

Account Number	7	9	9	2	7	3	9	8	7	1	x
Double every other	7	18	9	4	7	6	9	16	7	2	x
Sum digits	7	1+8=9	9	4	7	6	9	1+6=7	7	2	x

The calculated check digit is: x = 10 - (67 mod 10) = 3. So, the final account number is 79927398713.

To verify an account number we perform a similar process.

From the right-most digit, move left and double the value of every second digit. If the doubled number is greater than 9, then subtract 9 from the product (or add the digits together.)
Sum the digits of the resulting value in each position, call this value “s”.
If s mod 10 = 0, then the account number is valid.

Example of verifying the account number (with check digit):

Account number is 79927398713.

Account Number	7	9	9	2	7	3	9	8	7	1	3
Double every other	7	18	9	4	7	6	9	16	7	2	3
Sum digits	7	1+8=9	9	4	7	6	9	1+6=7	7	2	3

The sum is 70 and 70 mod 10 = 0, so the account number is valid.

Assignment Description

Complete the PHP program named project2.php. In this file, you will implement the verification process by implementing the following functions:

toDigits: takes an integer as input and returns an array of digits.
doubleEveryOther: takes an array of digits as input and returns a new array of integers where every other number is doubled starting at the right.
sumDigits: takes an array of integers and returns the sum of the digits of the numbers.
validate: takes an account number (integer) as input and returns true if the account number is valid, otherwise false.

Note that the program has a main function to call validate on user input. Do not change the main function.

Instructions

To start the assignment, login to your university Linux account and copy the assignment code to a location somewhere under your home directory. The assignment code is located at:

/export/home/public/schwesin/csc242/projects/project2-handout

You need to edit the project2.php file. Do not change the names of the file.

To submit your assignment, execute the following command from within your project2-handout directory:

    ~schwesin/bin/submit csc242 project2

Grading Criteria

Concise, accurate documentation following the CSC Department documentation guidelines
Correct implementation of the specification

Note: If the code has syntax errors or does not execute properly, you will receive a failing grade for this assignment. If the submission includes material that was not covered in class and the material is not properly cited, then you will receive a failing grade for this assignment.