Programming Exercise 5.31 - Mod 10 check: 

Credit card numbers follow certain patterns. A credit card number must have between 13 and 16 digits. It must start with:

• 4 for Visa cards
• 5 for Master cards
• 37 for American Express cards
• 6 for Discover cards

In 1954, Hans Luhn of IBM proposed an algorithm for validating credit card numbers. The algorithm is useful to determine if a card number is entered correctly or if a credit card is scanned correctly by a scanner. Almost all credit card numbers are generated following this validity check, commonly known as the Luhn check or the Mod 10 check, which can be described as follows (for illustration, consider the card number 4388576018402625): 

1. Double every second digit from right to left. If doubling of a digit results in a two-digit number, add up the two digits to get a single-digit number.
   2*2=4
   2*2=4
   4*2=8
   1*2=2
   6*2=12 (1+2=3)
   5*2=10 (1+0=1)
   8*2=16 (1+6=7)
   4*2=8
2. Now add all single-digit numbers from Step 1.
   4+4+8+2+3+1+7+8=37
3. Add all digits in the odd places from right to left in the card number.
   5+6+0+8+0+7+8+3=37
4. Sum the results from Setp 2 and Step 3.
   37+37=74.
5. If the result from Step 4 is divisible by 10, the card number is valid; otherwise, it is invalid. For example, the number 4388576018420625 is invalid, but the number 4388576018410707 is valid.

Write a program that begins with a credit card number as a long integer. Display whether the number is valid. Design your program to use the following methods:

/** Return true if the card number is valid */
public static boolean isValid(long number)

/** Extract a digit from the long*/
public static int separateDigit(long number, int position)
/* You can convert a long to a String and use String methods
OR
You can use modulus with division.*/

/** Get the result from Steps 1 and 2*/
public static int sumAndDoubleOfEvenPlace(long number)

/** Return this number if it is a single digit, otherwise, return the sum of the two digits */
public static int getAsOneDigit(int number)

/** Return sum of odd place digits in number, Step 3 */
public static int sumOfOddPlace(long number)
 
Feel free to add any other methods that you deem necessary!