Programming # 3 Solution

In this assignment you will learn about  loops and methods.  This assignment requires you to write a class named  CowsAndBulls.  This class must  be in a package named  pa3.

Note  that the  description  of a  programming assignment  is not  a  linear  narrative and  often

requires  multiple  readings  before  things  start to  click.   You  are  encouraged  to  consult  instruc- tors/Teaching Assistants for any questions/clarifications regarding  programming assignments.

 

 

1    Cows and Bulls

 

You might have played  the  game of Cows and  Bulls as a kid.  This  game consists  of two players, lets call them “Alice” and “Bob”.  The game starts by Alice picking a secret 4 digit number  so that all digits of the  number  are distinct. For  example,  Alice can pick 1024 but  is not  allowed to pick

1231. Bob’s goal is to find the secret number  that Alice has picked.  The game proceeds in rounds. In each round  Bob guesses a four digit number  and Alice gives a clue about  how close the guess is to the  secret  number.   Bob’s guess must  also have all distinct  digits.  Based on these  clues, in the next  round,  Bob guesses another  number.  The game proceeds till Bob finds the secret number.

Alice gives clue by specifying how many “cows” and “bulls’ are present in Bob’s guess. This is best illustrated by an example.  Suppose Alice’s secret number  is 1723 and Bob’s first guess is 2893. The digit 2 is present in both  the numbers.   However, it is the second digit of Alice’s number  and is the 4th digit of Bob’s number  (we are counting  from right to left).  Thus 2 is considered a “cow”. The  number  3 is also present  in both  the  numbers  and  it  is the  first digit  in both  the  numbers. So 3 is a “bull’.  Now, Alice’s tells Bob that there  is 1 cow and  1 bull in his guess.  Based on this information,  suppose Bob guessed 8923. This guess has 2 bulls (2 and 3) and 0 cows. So Alice tells Bob that there  are 0 cows and 2 bulls in his guess.  Suppose that Bob’s next  guess is 7112.  Since

7112 does not  have distinct  digits,  Alice responds  by telling that it is not  a valid guess.  Suppose Bob’s next  guess is 7123.  This  guess has 2 cows ( 7 and  1) and  2 bulls ( 2 and  3).  So Alice tells Bob that there  are 2 cows and 2 bulls.  Suppose Bob’s next  guess is 1723.  This  guess has 4 bulls, and thus  exactly  matches  the secret number,  and the game is Over.

 

 

2    Your Task

 

Your task  is to write a program  to play this game.  The program  takes  the role of “Alice” and the user takes the role of “Bob”.  When you run the program,  it will pick a secret 4-digit number  (with distinct  digits)  and interacts with the user.  For each guess the user types, the program  prints  the number  of cows and bulls.  The program  ends, when the user finds the secret number.

Your program  must behave as follows: At the beginning, it picks a random  4 digit number  (with all distinct  digits) and interacts with the user.  It prompts  the user to enter a valid guess. A guess is valid if all the digits of the guessed number  are distinct. For each valid guess the user entered,  the

program  outputs the number  of cows and bulls.  If the guess is not valid, then the program  outputs a message.  The program  repeatedly prompts  the user until  the user finds the secret number.

Hear is a sample run of the program:  Boldface letters  indicate  user input:

 

 

 

Welcome to Cows and Bulls Game. I picked a random 4-digit number with distinct integers, try finding it. Type your guess, must be a 4-digit number with distinct digits.

1780

Cows: 0 Bulls: 2

Type your guess, must be a 4-digit number with distinct digits

1084

Cows: 1 Bulls: 1

Type your guess, must be a 4-digit number with distinct digits

2316

Cows: 2 Bulls: 0

Type your guess, must be a 4-digit number with distinct digits

2216

Invalid guess. Type your guess, must be a 4-digit number with distinct digits

1680

Cows: 0 Bulls: 3

Type your guess, must be a 4-digit number with distinct digits

6180

Cows: 2 Bulls: 1

Type your guess, must be a 4-digit number with distinct digits

1170

Invalid guess. Type your guess, must be a 4-digit number with distinct digits

1670

Cows: 0 Bulls: 3

Type your guess, must be a 4-digit number with distinct digits

1650

Congratulations, You found the number, you took 9 guesses

 

 

 

We index digits from right to left (not  left to right) and indices start from 1 (not  from 0).  For example,  the first digit of 123 is 3. The digit 1 appears  at index 3 in 123.

You will write your program  by writing  several methods.  Your class CowsAndBulls must  have the following methods.  You are NOT allowed to use any of the String methods  in your code.

 

numDigits(int number). Takes  a positive  integer  number as a parameter and  returns the number  of digits in number. You may assume that number is always a positive integer,  and you do not have to write code to check this.

 

getDigit(int number, int i). Takes a positive integer number and an index i as parameters and returns the ith  digit (from right) of number. If number does not have ith  digit, then  it returns

−1. This method  must  make call(s) to numDigits. It may make call(s) to other  methods.You may

assume that number is always a positive integer,  and you do not have to write code to check this.

 

hasDistinctDigits(int number). Takes  a positive  integer  number as a parameter and  re- turns  true  if all the digits of number are distinct, otherwise  returns false. This method  must  make call(s) to getDigit. It may make call(s) to other methods.  You may assume that number is always a positive integer,  and you do not have to write code to check this.

 

indexOf(int number, int digit). Takes a positive integer  number and a digit as parame- ters and returns the position (from right) at which digit appears  in number, if number has distinct digits.  If number does not have distinct  digits, then this method  returns −2. If number has distinct digits,  and  digit does not  appear  in number, then  this  method  returns −1.  This  method  must make calls to hasDistinctDigits, numDigits and getDigit. It may make call(s) to other  meth- ods. You may assume that number is always a positive integer, and digit is a single digit number, and you do not have to write code to check this.

 

getCows(int first, int second). Takes  two  positive  integers  first and  second and  re- turns  the number  of cows between  the two numbers.  This method  must  make calls to numDigits, getDigit, and indexOf. It may make call(s) to other  methods.  You may assume that both  first and second are positive integers, and both first and second have distinct  digits.  You do not have to write code to check this.

 

getBulls(int first, int second). Takes  two  positive  integers  first and  second and  re- turns  the number  of bulls between  the two numbers.  This method  must  make calls to numDigits, getDigit, and indexOf. It may make call(s) to other  methods.  You may assume that both  first and second are positive integers, and both first and second have distinct  digits.  You do not have to write code to check this.

 

generateSecretNumber() This method  returns a randomly  chosen 4-digit number  whose dig- its are all distinct. This method  must  make a call to hasDistinctDigits.  It may make call(s) to other  methods.

 

main. This is the main method.  This method  must  do the following:

 

1.  Print a welcome message (see the sample run).

 

2.  Pick a secret number  by calling the method  generateSecretNumber

 

3.  Repeatedly  prompt  the  user  to  enter  a valid  guess until  the  guess matches  with  the  secret number.   For  each guess, if the  guess not  valid  (does not  have distinct  digits),  then  output a message saying so.  If the  guess is valid,  then  output the  number  of bulls (by  calling the method  getBulls) and number  of cows (by calling the method  getCows). Checking whether a guess is valid or not must  be performed  by making a call to hasDistinctDigits.

 

4.  When  user  finds the  secret  number,  display  number  of guesses that user  took  to  find the number,  and quit.

3    Generating Random Numbers

 

The method  generateSecretNumber requires  you to generate  a random  4-digit number.   You can use Random class of Java  for this.  Consider  the following code fragment:

 

 

Random r = new Random();

int x = r.nextInt(50);

 

r.nextInt(50) generates  a random  integer  between  0 and  49 (including  0 and  49).  Similarly r.nextInt(100) generates  a random  integer  in range [0, 99]. Note that this process may generate a number  whose digits are not distinct.

 

 

4    Coding Conventions

 

You must  follow good coding  conventions.    Variable  names  must  be meaningful,  variable  names (and  method  names)  must  start with  lower case letters,  code must  be properly  indented.  Your code must  have appropriate comments.   Failure  to follow good coding conventions  will cause you to lose points  (even if your solution  is correct).

 

 

5    Suggestions

 

For some of the methods  that you will be writing (getDigit, numDigits) you will be using integer division and modulus operators. We strongly suggest you to understand these operators  completely before you start coding.  You will gain some practice  on this in Recitation 7.

Do not  attempt to write  code for all the  methods  at  once.  Write  one method  at  a time,  test that the method  works correctly  then  proceed to the next  method.

Java  comes  with  many  in-built  methods.    You  are  NOT  allowed  to  use  any  of the  String methods.     In  addition,  you  are  NOT  allowed  to  use  methods   Math.pow, Integer.parseInt, Double.parseDouble.  If you use any of these methods,  you will lose points.

 

 

6    Specifications

 

You must  follow the specifications exactly.  Again, You are NOT allowed to use any String  method in  your  code.   If you  use String  methods,   you  will lose points.    Your  program  must  be  named CowsAndBulls and should be in a package named pa3.  Please note that Java  is case-sensitive.  The input-output behavior  of your program  must  be exactly  as described.  Failure  to follow the specifi- cations  (even if your solution  is correct)  will cause you to lose points.  Submit  CowsAndBulls.java via blackboard. Do not submit  CowsAndBulls.class.