CS 1301 Program 3 Fall 2014

Educational Goals: The educational goals of this program are that the student should use the concepts of

• design with pseudocode
• design of functions with various return types and parameters
• using mathematical operations to extract digits from numbers
• using for and while loops
• documentation
• testing with valid inputs and invalid inputs

Problem Description:

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 4388576018402626):

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.
   6 + 6 + 0 + 8 + 0 + 7 + 8 + 3 = 38
4. Sum the results from Step 2 and Step 3.
   37 + 38 = 75
5. If the result from Step 4 is divisible by 10, the card number is valid; otherwise, it is invalid. For example, the number 4388576018402626 is invalid, but the number 4388576018410707 is valid.

Sample interaction with the program:

Example run 1:
Enter a credit card number as a long integer: 4246345689049834
4246345689049834 is invalid



Example run 2:
Enter a credit card number as a long integer: 4388576018410707
4388576018410707 is valid

Notes:

• You have to have a static method named isValid, with a bool return value and a parameter of type long for the credit card number
• You have to have a static method named getDigit, with an int return value and a parameter of type int. This function returns the argument if it is a single digit, otherwise, returns the sum of the two digits.
• You have to have a static method named sumOfDoubleEvenPlace, int return value and one parameter of type long. This function returns the result from step 2.
• You have to have a static method named sumOfOddPlace, int return value and one parameter of type long. The function will return the sum of odd place digits in the number.
• You have to have a static method named getSize, int return value and one parameter of type long that returns the number of digits in the argument
• You have to have a static method named getPrefix, long return value and two parameters: one long (number) and one int (k) that returns the first k number of digits from number. If the number of digits in number is less than k, return number.
• You have to have a static method named prefixMatched, boolean return value and two parameters: long (number) and int (d). The function returns true if the digit d is a prefix for number.

  public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    
    System.out.print("Enter a credit card number as a long integer: ");
    long number = input.nextLong();
    
    if (isValid(number))
      System.out.println(number + " is valid");
    else
      System.out.println(number + " is invalid"); 
  }

Test Cases

First, read the assignment carefully. Look for how the program is supposed to behave. You do not know what the code looks like - that is fine. The assignment gives some examples of normal runs. There are other test cases needed. Create a test case table similar to that of program 1. The test cases are due at the same time your design and code are due.

Design

// main function
// step 1: prompt for credit card number 
// ... enter your steps here
// compute things
// output things


// isValid function
// step 1: 
// step 2:
// fill in the rest of the design

//  design the other functions
...

Implement the design

There are several specifications about how your program should be written.

• you need to use counters and loops
• make sure you format the lines of the output as described. The line breaks and the punctuation should be as shown. The output messages should be exactly as given.

Please read the documentation standard on the class web page. As you can see from looking at the grading criteria, we will be looking to see how you meet these standards. Note particularly that we require a prolog!

Remember that the program must run with NO errors or warnings. If it does not, it will not be graded!