Computer Programming in Java home > 11.12 Credit Card Check Digit 11.12 Credit Card Check Digit* Banks issue credit cards with 16 digit numbers. If you've never thought about it before you may not realize it, but there are specific rules for what those numbers can be. For example, the first few digits of the number tell you what kind of card it is -all Visa cards start with 4. MasterCard numbers start with 51 through 55, American Express starts with 34 or 37, etc. Automated systems can use this number to tell which company to contact without having to look at the card itself and see what the bank is on it. Another key part of the credit card number standard is the check digit. The last digit of every credit card number is determined by the previous 15 digits through a simple mathematical formula known the Luhn Algorithm The Lhun Algorithm can be used to check if a credit card number has been corrupted in its transmission between the vendor reading the card, and the bank which has the account. It can also be used to check to see if a credit card number is valid before transmitting it to the bank, The Luhn Algorithm is described at the link above, but the basic idea is From the right-to-left, double the value of each digit that is in an even-numbered position (with the check-digit at position 1) If this doubling gives you a two-digit value for any of the numbers, then subtract 9 from the value (which is easier than adding the digits together but gets you the same result). Leave the odd valued positions as is 2. Sum together all of the values except the check digit 3. Take the digit in the one's position of the sum. If the value of that digit is 0. then it stays as 0 If the value is greater than zero. subtract that value from 10. That value should be the check digit (note that the special case for is required since '10's not a single dat For example, suppose the card you want to Valldate 5457623898234113. In this case the check-digit is 3 and the remaining digits are the 15-digit account number we can confirm that we likely have a good card number by Validating the check digit as follows Position 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 Origina Value 5 4 517 6 2 389 8 2 3 4 Doubled value 10 10 12 6 18 Doubled-value adjusted 3 6 9 5 6 3 2 ON 9 8 2 4 1 7 Original Value 5 4 239 8234 Doubled value 10 10 12. 6 18 4 8 Doubled-value adjusted 1 1 3 9 4 8 2 Sum of values - 67 1 4 7 3 2 6 8 9 8 43 81 2 Check digit is 3 (10-7-3) You can read more about credit card numbers, as well as how the Luhn Algorithm is used in other areas of Computer Science. In this article from the Data Genetics blog (where the above example was taken from) For this lab you will write a Java program that checks credit card strings to see if they are valid. Your program should first prompt the user to enter a string of numbers as a credit card number or enter a blank line to quit the program If the user doesn't quit, your program should ensure that this string is exactly 16 characters in length. If the user enters a string that is not 16 characters in length your program should print an error message and ask again for a valid string. Your program should use the Luhn Algorithm above to compute what the check digit should be and then compare it to the actual value in the provided string and report whether the credit card number is valid or wrong. If it is wrong your program should report what the correct check digit should be for the input value. Your program should keep asking for new values until the user enters a blank line to quit the program. Create a new project named LuhnAlgorithm and a new Java program in that project folder named LahnAlgorithm, java for this project. You can find a selection of valid-but-fake credit card numbers courtesy of PayPal at this link. Change the check digit on any of them to get an invalid number (note that your code should only use the 16 digit numbers and does not have to account for any of the card numbers that have any number of digits other that NOTE: You do NOT need to use arrays to solve this problem - this problem can be som with nested loops Solutions that use an array where it isnt needed will be penalized into ways: First, you're making the problem much harder than it needs to be and second there will be a point deduction for use of an unnecessary array in the solution SampleOutput: This is a sample transcript of what your program should do. Items in bold are user input and should not be put on the screen by your program Enter credit card number Center a blank line to quit): 5457623898234112 Check dicit should be 3 Check dicit is 2 Humber is not valid Enter a credit card nunber Center blank line to quit): 5457623898234113 Check digit should be 3 Check digit is: 3 Number is valid Enter credit card number (enter blank line to quit): 5555555555554 ERROR! Number MUST have exactly 16 digits Enter a credit card number Center a blank line to quit) 55 Check digit should be 4 Check digit is 5 Number is not valid. Enter a credit card number Center blank line to quit) Goodbye! Note: You will need to convert characters in your string into integer values to make this project work. There are two ways to do this. The first is to use Integer.parseInt and substring to get a character value. The following lines of code would give you the integer value of the first character of the string input String 3 input.substring(0, 1); ant val = Integer.parseInt(s); Another way to get a numeric value from a character is to use the method Character, getunericValue This takes a char value (not a String) and converts it to the correct integer value. The following lines of code would give the integer value of the character of the String input char input.charAt(0); int val - Character.getNumeraValue (e) 245918. 1550866 LuhnAlgorithm.java Sum=; char pos = credit.charAt(num); int pos Int=Character.getNumericValue(pos); if(num%2==0){ num=num*2;} if(posInt>=10){ posInt=posInt-9; } sum-sum+pos Int;} checkcc-Integer.parseInt(credit.substring(15,16)); Character.getNumericValue(checkcC); checkCC=Integer.parseInt(credit.sbstring(num, num+1)); Character.getNumericValue(checke); System.out.print(\"Check digit should be: \"checkcC); System.out.print(\"Check digit is: \"+sum); } if(checkcCa=sum) { System.out.println(\"Number is valid.\");} elset System.out.println(\"Number is not valid.\"); } System.out.println(); 5 6 Develop mode Submit mode Run your program as often as you'd like before submitting for grading input values in the first box then click Run program and observe the pro second hox G lenovo LuhnAlgorithm.java >ystem.out.prinLL CHLer d creul caru numuerencer d Uldrik Ime U qur): ) String credit - keyboard.nextLine(); int num = credit. length()-1; int sum=0; int checkcC=; while(credit.length()>0){ if (credit.length() !=16){ System.out.print(\"ERROR! Number MUST have exactly 16 digits.\"); System.out.println(); System.out.print(\"Enter a cifedit card number(enter a blank line to quit): \"); credit = keyboard.nextLine(); } else{ for(num=credit.length()-2;num>=0; --num) { Sum=@; char pos = credit.charAt(num); int pos Int-Character.getNumericValue(pos); if(num%2==0){ num=num*2;} if (posInt>=10){ posInt=pos Int-9;} sum=sum+posInt;} check-Integer.parseInt(credit.substring(15,16)); velop mode Submit mode Run your program as often as you'd like, before submitting for grading B input values in the first box, then click Run program and observe the prog second hox ,~ ULCIS LUI UE. FU Calpie, Huy TULILunel, Dulcie uie apelu the first few digits of the number tell you what kind of card it is-all Visa cards start with 4. MasterCard numbers start with 51 through 55, American Express starts with 34 or 37, etc. Automated systems can use this number to tell which company to contact without having to \"lookat the card itself and see what the bank is on it. Another key part of the credit card number standard is the check digit. The last digit of every credit card number is determined by the previous 15 digits through a simple mathematical formula known the Luhn Algorithm. The Lhun Algorithm can be used to check if a credit card number has been corrupted in its transmission between the vendor reading the card, and the bank which has the account. It can also be used to check to see if a credit card number is valid before transmitting it to the bank. The Luhn Algorithm is described at the link above, but the basic idea is: 1. From the right-to-left, double the value of each digit that is in an even-numbered position (with the check-digit at position 1). If this doubling gives you a two-digit value for any of the numbers, then subtract 9 from the value (which is easier than adding the digits together but gets you the same result). Leave the odd-valued positions as is. 2. Sum together all of the values except the check digit. 3. Take the digit in the one's position of the sum. If the value of that digit is 0, then it stays as 0. If the value is greater than zero, subtract that value from 10. That value should be the check digit (note that the special case for O is required since \"10\" is not a single digit). For example, suppose the card you want to validate is: 5457623898234113. In this case the check-digit is 3 and the remaining digits are the 15-digit account number. We can confirm that we likely have a good card number by validating the check digit as follows: Position 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 Original Value 5 5 7 6 2 3 8 9 8 2 3 4 1 1 3 Doubled value 10 10 12 6 18 2 4 6 4 B 2 Doubled-value adjusted 1 1 3 6 9 4 8 2 Sum of values 67 1 4 1 7 3 2 6 8 9 8 4 3 8 12 Check digit is 3 (10-7 - 3) You can read more about credit card numbers, as well as how the Luhn Algorithm is used in other areas of Computer Science, in this article from the Data Genetics blog (where the above example was taken from). For this lab you will write a Java program that checks credit card strings to see if they are valid. Your program should first prompt the user to enter a string of numbers as a credit card number, or enter a blank line to quit the program. If the user doesn't quit, your program should ensure that this string is exactly 16 characters in length. If the user enters a string that is not 16 characters in length, your program should print an error message and ask again for a valid string. Your program should use the Luhn Algorithm above to compute what the check digit should be and then compare it to the actual value in the provided string and report whether the credit card number is valid or wrong. If it is wrong, your program should report what the correct check digit should be for the input value. Your program should keep asking for new values until the user enters a blank line to quit the program. Create a new project named LuhnAlgorithm and a new Java program in that project folder named Lahnalgorithm.java for this project. You can find a selection of valid-but-fake credit card numbers courtesy of PayPal at this link. Change the check digit on any of them to get an invalid number (note that your code should only use the 16 digit numbers and does not have to account for any of the card numbers that have any number of digits other than 16). NOTE: You do NOT need to use arrays to solve this problem - this problem can be solved just with nested loops. Solutions that use an array where it isnt needed will be penalized in two ways: First, you're making the problem much harder than it needs to be and second there will be a point deduction for use of an unnecessary array in the solution Sample Output: This is a sample transcript of what your program should do. Items in bold are user input and should not be put on the screen by your program Enter a credit card number Center a blank line to quit): 5457623898234112 Check digit should be 3 Check digit is! 2 Number is not valid Enter credit card aber Center a blank line to quit 5457623898234113 Check dicit should be 3 Check digitis: 3 will be a point deduction for use of an unnecessary array in the solution. Sample Output: This is a sample transcript of what your program should do. Items in bold are user input and should not be put on the screen by your program. Enter a credit card number (enter a blank line to quit): 5457623898234112 Check digit should be: 3 Check digit is: 2 Number is not valid. Enter a credit card number Center a blank line to quit): 5457623898234113 Check digit should be: 3 Check digit is: 3 Number is valid Enter a credit card number (enter a blank line to quit): 5555555555554 ERROR! Number MUST have exactly 16 digits. 555555554445 Enter a credit card number Center a blank line to quit): 55 Check digit should be: 4 Check digit is: 5 Number is not valid. Enter a credit card number Center a blank line to quit): Goodbye! Note: You will need to convert characters in your string into integer values to make this project work. There are two ways to do this. The first is to use Integer parseInt and substring to get a character value. The following lines of code would give you the integer value of the first character of the string input Check digit should be: 4 Check digit is: 5 Number is not valid. Enter a credit card number (enter a blank line to quit): Goodbye! Note: You will need to convert characters in your string into integer values to make this project work. There are two ways to do this. The first is to use Integer.parseInt and substring to get a character value. The following lines of code would give you the integer value of the first character of the string input: String 3 = input.substring(0,1); int val = Integer.parseInt(s); Another way to get a numeric value from a character is to use the method Character. get NumericValue. This takes a char value (not a String) and converts it to its correct integer value. The following lines of code would give the integer value of the first character of the String input: char c = input.charAt(0); int val = Character.getNumericValue (c): 245918.1550866 LAB 11.12.1: Credit Card Check Digit LAB ACTIVITY 8/22 Load default template LuhnAlgorithm java GES YUH! JavaSULTORICI public class LuhnAlgorithm { 5 5 7 8 9 1 2 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 public static void main(String[] args) { Scanner keyboard - new Scanner(System.in); System.out.print(\"Enter a credit card number (enter a blank line to quit): \"); String credit - keyboard.nextLine(); int num = credit.length()-1; int sum- int checkcc-; while(credit.length()>0){ if (credit.length()!-16){ System.out.print(\"ERROR! Number MUST have exactly 16 digits.\"); System.out.println(); System.out.print(\"Enter a credit card number(enter a blank line to quit): \"); credit - keyboard.nextLine();} else{ for(num=credit.length()-2;num>=;--nun) { sum-e; char pos - credit.charAt(num); int pos Int-Character.getNumericValue (pos); if(num2) num.num.2;) if (pos Int-10) posInt posInt-9;} sum sumpos Int;} checkcc-Integer.parseInt(credit.substring(15,16)); Character.getNumericValue(checkcc); check-Integer.parseInt(credit.substring(num, nun+1)); Character.getNumericValue(checkc); System.out.print(\"Check digit should be: \"+checkc); System.out.print(\"Check digit is: \"+sum);} if (checksum) { System.out.println(\"Number is valid.\"); } elset System.out.println(\"Number is not valid.\"); } System.out.println(); 42 45 Banks issue credit cards with 16 digit numbers. If you've never thought about it before you may not realize it, but there are specific rules for what those numbers can be. For example, the first few digits of the number tell you what kind of card it is -all Visa cards start with 4. MasterCard numbers start with 51 through 55, American Express starts with 34 or 37, etc. Automated systems can use this number to tell which company to contact without having to \"look\" at the card itself and see what the bank is on it. Another key part of the credit card number standard is the check digit. The last digit of every credit card number is determined by the previous 15 digits through a simple mathematical formula known the Luhn Algorithm. The Lhun Algorithm can be used to check if a credit card number has been corrupted in its transmission between the vendor reading the card, and the bank which has the account. It can also be used to check to see if a credit card number is valid before transmitting it to the bank. The Luhn Algorithm is described at the link above, but the basic idea is: 1. From the right-to-left, double the value of each digit that is in an even-numbered position (with the check-digit at position 1). If this doubling gives you a two-digit value for any of the numbers, then subtract 9 from the value (which is easier than adding the digits together but gets you the same result). Leave the odd-valued positions as is. 2. Sum together all of the values except the check digit. 3. Take the digit in the one's position of the sum. If the value of that digit is o, then it stays as 0. If the value is greater than zero, subtract that value from 10. That value should be the check digit (note that the special case for O is required since \"10\" is not a single digit). For example, suppose the card you want to validate is: 5457623898234113. In this case the check-digit is 3 and the remaining digits are the 15-digit account number. We can confirm that we likely have a good card number by validating the check digit as follows: Position 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 Original Value 5 4 5 7 6 2 3 8 9 8 2 3 4 1 1 3 Doubled value 8 2 Doubled-value adjusted 1 6 8 2 Sum of values = 67 7 2 6 8 9 8 4 3 8 1 2 Check digit is 3 (10-7 = 3) 10 10 12 6 4 8 18 9 2 2 1 3 4 1 4 1 3 You can read more about credit card numbers, as well as how the Luhn Algorithm is used in other areas of Computer Science in this article from the Data Genetics blog (where the above example was taken from). For this lab you will write a Java program that checks credit card strings to see if they are valid. Your program should first prompt the user to enter a string of numbers as a credit card number, or enter a blank line to quit the program. If the user doesn't quit, your program should ensure that this string is exactly 16 characters in length. If the user enters a string that is not 16 characters in length, your program should print an error message and ask again for a valid string. Your program should use the Luhn Algorithm above to compute what the check digit should be and then compare it to the actual value in the provided string and report whether the credit card number is valid or wrong. If it is wrong, your program should report what the correct check digit should be for the input value. Your program should keep asking for new values until the user enters a blank line to quit the program. Create a new project named Luhnalgorithm and a new Java program in that project folder named Luhnalgorithm. java for this project. You can find a selection of valid-but-fake credit card numbers courtesy of PayPal at this link. Change the check digit on any of them to get an invalid number (note that your code should only use the 16 digit numbers and does not have to account for any of the card numbers that have any number of digits other than 16). NOTE: You do NOT need to use arrays to solve this problem - this problem can be solved just with nested loops. Solutions that use an array where it isn't needed will be penalized in two ways: First, you're making the problem much harder than it needs to be, and second there will be a point deduction for use of an unnecessary array in the solution. Sample Output: This is a sample transcript of what your program should do. Items in bold are user input and should not be put on the screen by your program. Enter a credit card number (enter a blank line to quit): 5457623898234112 Check digit should be: 3 Check digit is: 2 Number is not valid. Enter a credit card number (enter a blank line to quit): 5457623898234113 Check digit should be: 3 Check digit is: 3 Number is valid Enter a credit card number (enter a blank line to quit): 5555555555554 ERROR! Number MUST have exactly 16 digits. Enter a credit card number (enter a blank line to quit): 5555555555554445 Check digit should be: 4 Check digit is: 5 Number is not valid. Enter a credit card number (enter a blank line to quit): Goodbye! Note: You will need to convert characters in your string into integer values to make this project work. There are two ways to do this. The first is to use Integer.parseInt and substring to get a character value. The following lines of code would give you the integer value of the first character of the string input: String 3 = input.substring(0,1); int val = Integer.parseInt(s); Another way to get a numeric value from a character is to use the method Character.getNumericValue. This takes a char value (not a String) and converts it to its correct integer value. The following lines of code would give the integer value of the first character of the String input: char c = input.charAt(0); int val = Character.getNumericValue (c); 245918.1550866