JAC 444 Workshop 2 solution

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Task 1:Write a hangman game that randomly generates a word and prompts the user to guess
one letter at a time, as shown in the sample run. Each letter in the word is displayed as an
asterisk. When the user makes a correct guess, the actual letter is then displayed. When the
user finishes a word, display the number of misses and ask the user whether to continue to play
with another word. Declare an array to store words, as follows:
// Add any words you wish in this array
String[] words = {“write”, “that”, …};
JAC – 444
Task 2: Design a class named Location for locating a maximal value and its location in a twodimensional array. The class contains data field’s row, column, and maxValue that store the
maximal value and its indices in a two-dimensional array with row and column and maxValue
as a double type.
Write the following method that returns the location of the largest element in a twodimensional array:
public static Location locateLargest(double[][] a)
The return value is an instance of Location. Write a test program that prompts the user to enter
a two-dimensional array and displays the location of the largest element in the array. Here is a
sample run:
Task 3: 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
JAC – 444
In 1954, Hans Luhn of IBM proposed an algorithm for validating credit card numbers. The
algorithm is useful to determine whether a card number is entered correctly or whether a
credit card is scanned correctly by a scanner. 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. 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.
Write a program that prompts the user to enter a credit card number as a long integer (can also
use string to solve this). Display whether the number is valid or invalid. Design your program to
create and use the following methods:
1. A method which should: Return true if the card number is valid
2. A method which should: Get the result from Step 2
3. A method which should: Return this number if it is a single digit, otherwise, return the
sum of the two digits
4. A method which should: Return sum of odd-place digits in number
5. A method which should: Return true if the digit is a prefix for number
6. A method which should: Return the number of digits
7. A method which should: Return the first k number of digits from number. If the number
of digits in number is less than k, return number.
Here are sample runs of the program: