created 01/24/99; revised 07/31/07, 10/20/08, 11/04/2012, 07/13/22, 12/20/2022
It is spring, and you plant 10 seedling tomato plants. The probability that an individual plant will survive through summer is 0.9. How many of your 10 plants will survive?
Write a program that simulates this. Loop 10 times (once per plant.) For each plant, throw a 10-sided die. If the face is 1 through 9, the plant survives.
Of course, different runs of the program will produce a variety of results. Run the program a number of times and calculate the average number of plants that survive the season. Or, better yet, write the program so that it calculates the average survival for 100 simulated seasons.
Write a program that implements a guessing game. This is a "classic" program, frequently assigned in beginning CS classes.
The program picks a random number from 1 to 10. Now the user gets three guesses. As soon as the user enters the correct number the program writes a winning message and exits. If the user fails to enter the correct number in three guesses, the program writes a failure message and exits.
Use methods of the Random class.
Here are two example runs of the program:
C:\>java GuessingGame I am thinking of a number from 1 to 10. You must guess what it is in three tries. Enter a guess: 4 wrong 8 RIGHT! You have won the game. C:\>java GuessingGame I am thinking of a number from 1 to 10. You must guess what it is in three tries. Enter a guess: 1 wrong 5 wrong 9 wrong The correct number was 7. You have lost the game.
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Write a more complicated guessing game, similar to the one in Exercise 2, but now the program is to write "cold" when the guess is 3 or more away from the correct answer, "warm" when the guess is 2 away, and "hot" when the guess is 1 away. As soon as the user enters the correct number the program writes a winning message and exits. For example:
C:\>java GuessingGame I am thinking of a number from 1 to 10. You must guess what it is in three tries. Enter a guess: 1 cold 5 RIGHT! You have won the game. C:\>java GuessingGame I am thinking of a number from 1 to 10. You must guess what it is in three tries. Enter a guess: 4 cold 5 cold 8 wrong. The correct number was 9. You have lost the game. C:\>java GuessingGame I am thinking of a number from 1 to 10. You must guess what it is in three tries. Enter a guess: 4 hot 5 warm 3 RIGHT! You have won the game.
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(Game suggested by Anthony Ma.)
The player starts with a score of 5 points. As before, the player must guess a number from 1 to 10. Each time the user guesses a point is subtracted from their score.
If the score becomes negative, the player has lost the game. It the user enters the correct number the program writes writes out the score and winning message. Examples:
C:\>java GuessingGame I am thinking of a number from 1 to 10. Try to guess the number. Your beginning score is 5 points. Each time you guess wrong, your score is decreased by one. Enter a guess: 5 Too Low! Your score is now 4 Enter a guess: 7 Too Low! Your score is now 3 Enter a guess: 8 You WON the game! Your score is 3 C:\>java GuessingGame I am thinking of a number from 1 to 10. Try to guess the number. Your beginning score is 5 points. Each time you guess wrong, your score is decreased by one. Enter a guess: 3 Too Low! Your score is now 4 Enter a guess: 4 Too Low! Your score is now 3 Enter a guess: 5 Too Low! Your score is now 2 Enter a guess: 6 Too Low! Your score is now 1 Enter a guess: 7 Too Low! Your score is now 0 You lost. Your score is 0
The Math.abs() method useful might be useful for this.
To make the game more challenging, make the range of numbers 1 to 100.
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Write an even more complicated guessing game. In this version, the full game consists of 10 "rounds," where each round is a game like exercise 3. After the 10 rounds, the program prints out how many of the 10 rounds were won and how many were lost.
Here is an example run:
C:\>java GuessingGame round 1: I am thinking of a number from 1 to 10. You must guess what it is in three tries. Enter a guess: 4 hot 5 RIGHT! You have won 1 out of 1 rounds. round 2: I am thinking of a number from 1 to 10. You must guess what it is in three tries. Enter a guess: 10 cold 5 cold 3 wrong The correct number was 1 You have won 1 out of 2 rounds. . . . round 10: I am thinking of a number from 1 to 10. You must guess what it is in three tries. Enter a guess: 1 cold 6 warm 8 RIGHT! You have won 7 out of 10 rounds. Your rating: amateur. C:\>
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This exercise is based on the PasswordGenerator program in the chapter.
To improve the password, edit the string of characters choices
so that it contains more digits, increasing the chances that digits will be picked.
Do this by appending "1234567890" several more times on to the end of choices.
There is no need for choices to contain only one of each character.
If you want punctuation your passwords, append those characters to the string, as well.
Another improvement is to require that a password have at least one digit. There are several ways in which this can be done. Don't assume that the required digit in a password will be in a fixed location.
A further improvement is the rule that every consonant must be followed by a vowel of the same case. This will make passwords easier to memorize. Of course, it also makes them easier to guess, especially if a cracker knows that this rule is being used.
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A password generator can also be used as a password cracker. Essentially, the generator keeps creating passwords until it finds one that works. (This is why a logon attempt is often rejected if the password fails three times.)
Write a program that asks the user for a password. The user enters a password (which must be short). Now pretend that this password is a secret from the rest of the program, which must try to guess it. The program then uses the password generator repeatedly until a randomly generated password matches the password the user entered. Assume that the user's password is five characters or less (otherwise the program will run for eons). Write out the number attempts it took to find the password. Here are some example runs:
K:\cai\>java PasswordCracker Enter a "secret" password-->ant Here is your password: ant It took 2181892 tries to guess it K:\cai\>java PasswordCracker Enter a "secret" password-->rats Here is your password: rats It took 10956100 tries to guess it K:\cai\>java PasswordCracker Enter a "secret" password-->frog Here is your password: frog It took 91555945 tries to guess it K:\cai\>java PasswordCracker Enter a "secret" password-->moose Here is your password: moose It took 279530402 tries to guess it
A better cracker program would systematically generate all possible one-letter passwords, then all possible two-letter passwords, then all possible three-letter passwords,..., and so on, comparing each one to the secret password. This program is hard to write without arrays (a subject of a future chapter).
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The average of the 1000 integers from 0 to 1000 is 500. The the integers 0 to 499 are on one side of 500 and the integers 501 to 1000 are on the other sided. So the average of a sample of integers randomly selected from the range [0,1000] should be about 500.
Write a program that asks the user for N and then computes the average of N
integers selected from [0,1000]. Note that both zero and one thousand are included in the range.
Compute the average as a double precision value.
Of course, each time you run the program for the same N you will most likely get a different result.
Run the program for different values of N (and several times for each N) and
observe how close the values are to 500.
Random may generate the same values more than once, so even if N is 1000 the average
will not be exactly 500.
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A one dimensional random walk is where a particle starts out at X=0.0, then moves right or left along the X axis by random amounts. Note that X can be negative or positive (or zero). Think of it as a bead an a string, randomly being shaken back and forth.
Write a program that initializes to zero a variable X,
representing the position of the bead, then
repeatedly adds random amounts in the range (-1.0, +1.0) to X.
The program stops after a specified number of iterations.
You will need to use the nextDouble() method of Random
and transform it to match the specified range.
How distant from its starting position is X after 100 iterations?
1000?
What is the maximum distance it coule be? How likely is that?
K:\cai\>java RandomWalkOneDim How many iterations? 100 After 100 moves X is now at 1.1190381131949723 K:\cai\>java RandomWalkOneDim How many iterations? 1000 After 1000 moves X is now at -0.4633309201402265
Change the program so that it keeps iterating until the bead reaches a particular
distance (positive or negative) from the origin.
Use Math.abs() to determine the distance.
If you pick a large distance, you may have to kill the running program, since
the distance may never be reached.
(On Windows systems, do this with control-D in the DOS window.)
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A two dimensional random walk is where a particle starts out at X=0.0, Y=0.0 then moves by small random increments in both X and Y. Think of it as a confused ant, randomly walking on the 2D plane.
Write a program that initializes to zero two variables X and Y,
representing the position of the ant, then
repeatedly adds random amounts in the range (-1.0, +1.0) to each of them.
Pick two random amounts, one for X and one for Y.
The program stops after a specified number of iterations
and prints out the values of the coordinates and the final distance of the ant from the origin.
Use the Pythagorean formula to calculate the distance:
_______
distance = \/X2 + Y2
There are plenty of variations on this program, for instance, counting the iterations it takes to reach a certain distance. Or, implement two ants, each with its own coordinates, which both start out at (0, 0) and wander for 1000 steps. How far apart are the ants? If one ant does not move, will they be closer or further apart than when they both move?
Of course, another variation is to implement a 3D random walk,
with independent variables X, Y, and Z.
Think of this as a confused firefly, fluttering randomly through the night.
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Write a program that implements a two player game. The computer is the score keeper and the two players are humans. Each round of the game starts with the computer randomly picking a double precision number from 1.0 to slightly less than 100.0. Each player estimates the square root of the number and enters the estimate. The player who's estimate is closest to correct wins the round. Players alternate who goes first in each round. Play ends after a specified number of rounds.
How many rounds? 4 First Player, sign in--> Dweezle Secnd Player, sign in--> Moon Unit What is the square root of 83.29097831183603 ? Dweezle, your guess: 9.1 Moon Unit, your guess: 9.2 The correct square root: 9.126389116832353 Dweezle is 0.026389116832353565 away Moon Unit is 0.07361088316764608 away Dweezle wins! What is the square root of 87.79346957866132 ? Moon Unit, your guess: 8.8 Dweezle, your guess: 8.9 The correct square root: 9.36981694477866 Dweezle is 0.46981694477866043 away Moon Unit is 0.5698169447786601 away Dweezle wins! What is the square root of 67.44682032701256 ? Dweezle, your guess: 8.2 Moon Unit, your guess: 8.1 The correct square root: 8.212601313044033 Dweezle is 0.012601313044033446 away Moon Unit is 0.11260131304403309 away Dweezle wins! What is the square root of 71.64725527288849 ? Moon Unit, your guess: 8.4 Dweezle, your guess: 8.45 The correct square root: 8.464470170831042 Dweezle is 0.01447017083104285 away Moon Unit is 0.06447017083104178 away Dweezle wins! ---- Final Score ---- Dweezle: 4 Moon Unit: 0
Call Scanner.nextLine() to read in the end of line characters after
the number of iterations.
Then read in the player names using Scanner.nextLine().
Use nextDouble() for the estimates.
Math.abs() and Math.sqrt() will be useful.
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This is a dice game similar to the game Pig, but easier to implement. The player plays against the computer.
In a genuine Pig game, the computer would repeatedly throw a single die (just like the player) and use strategy to determine when to stop.
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