Category Archives: Computer Science

Luhn Check Assignment

Luhn Check

It is possible to tell if a number could be a valid credit card. Credit cards numbers can be validated against an algorithm known as a Luhn.  Read this first.

Luhn Number Generator

 

http://www.datagenetics.com/blog/july42013/index.html

Counting from the check digit, which is the rightmost, and moving left, double the value of every second digit.

Sum the digits of the products together with the undoubled digits from the original number.

If the total ends in 0 (put another way, if the total modulo 10 is congruent to 0), then the number is valid according to the Luhn formula; else it is not valid.

 

from : http://www.impuls-imaging.com/wp-content/uploads/2013/07/luhn_algorithm.png

from : http://www.impuls-imaging.com/wp-content/uploads/2013/07/luhn_algorithm.png

Image from http://www.impuls-imaging.com/wp-content/uploads/2013/07/luhn_algorithm.png

Mod 10+5 Variant Some credit cards use the “Mod 10 plus 5” variant to extend the space of valid card numbers.[citation needed] In this variant, if the sum ends in 0 or 5, the number is considered valid.

from http://www.moneybluebook.com/imagesvr_ce/mbb/luhn-amex-calculation.jpg

from http://www.moneybluebook.com/imagesvr_ce/mbb/luhn-amex-calculation.jpg

from http://www.moneybluebook.com/imagesvr_ce/mbb/luhn-amex-calculation.jpg

 

 

A more extensive analysis with good images and an online Luhn Checker  (currently blocked by Harrison network filter)

Jeroo Walk The Lake with Loops

 

Original Project Descriptions is here

Acknowledgement This problem is adapted from one that was created originally by Erica Eddy of The University of Wisconsin – Parkside.

Your jeroo is exploring the outer perimeter of the lake. It starts next to a flower and travels the entire way around the lake. Have your jeroo stop immediately before the flower (using a loop) and then, after the loop is over,  your jeroo should pick the flower.

Downloaddownload-bttn the maps

Map #1 : rectangular-lake.jev arrow_right_large
recangular-lake-if2.jev arrow_right_large  
For this one, your Jeroo should travel around the entire outer rim of the island and stop immediately before the flower.
rim-of-lake-1.jev
arrow_right_large  
rectangular-lake-bumps1.jev
 arrow_right_large  
Remember Nets kill Jeroosrectangular-lake-bumps2.jev arrow_right_large  
Write a loop that makes the jeroo travel around the lake below. This loop should never end. walk-the-lake-jacks-map.jevs

Printing Digits Of Numbers in Java Assignment

Let’s write the following method

public void printDigits( int n){

}

 

Walk through of how the code should work:

the algorithm inolves

1) extract last digit

2) print last digit

3) remove last digit

keep doing this until there are no more digits

print-numbrs-screen-shot

Example :

Let’s look at printDigits( 345)

Walk through of how the code should work:

the algorithm inolves

1) extract last digit ‘5’

2) print last digit print ‘5’

3) remove last digit now n should be ’34’

do this for ‘4’ and then ‘3’ until there are no more digits

You need a while loop. Think about it. What is the value of n when there are no more digits?