Develop Reference

How do I include a question asking the user if they want to play again?

I am still new to Java and as such I am still figuring some things out. I have been having issues with including code asking the user if they want to play again. I have attempted putting it in the main class in a print statement which gave me an error. After that, I attempted putting it in the Guess.java class in multpile places but I just recieved errors. I have read up on the issue and some sites have suggested a while loop but I am unsure how to implement it into my current code. I have included both the main class which is called GuessingGame.java and the Guess.java class below. Thank you for any assistance that can be provided.
GuessingGame.java
public class GuessingGame {
public static void main(String[] args) {
new Guess().doGuess();
}
}
Guess.java
class Guess {
private int answer = 0;
int tries = 0;
Scanner input = new Scanner(System.in);
int guess, i;
boolean win = false;
int amount = 10;
public Guess() {
answer = generateRandomNumber();
}
//Generate a private number between 1 and a thousand
private int generateRandomNumber() {
Random rand = new Random();
return rand.nextInt(1000) + 1;
}
public void doGuess() {
while (!win) {
System.out.println("You are limited to ten attempts."
+ " Guess a number between 1 and 1000: ");
guess = input.nextInt();
if (tries > 9) {
System.out.println("You should be able to do better!"
+ " You have hit your ten guess limit. The number"
+ " was: " + answer);
System.out.println("Do you want to play again?: ");
return;
}
if (guess > 1000) {
System.out.println("Your guess is out of the range!");
} else if (guess < 1) {
System.out.println("Your guess is out of the range!");
} else if (guess == answer) {
win = true;
tries++;
} else if (guess < answer && i != amount - 1) {
System.out.println("Your guess is too low!");
tries++;
} else if (guess > answer && i != amount - 1) {
System.out.println("Your guess is too high!");
tries++;
}
}
System.out.println("Congragulations! You guessed the number!"
+ "The number was: " + answer);
System.out.println("It took you " + tries + " tries");
}
}

You already found a good position for adding this functionality:
System.out.println("Do you want to play again?: ");
The first step now is to also tell the user what he/she should enter after that question:
System.out.println("Do you want to play again? (enter 0 for yes and 1 for no): ");
After that we need to get the user input of course:
int number;
//If the user enters e.g. a string instead of a number, the InputMismatchException
//will be thrown and the catch-block will be executed
try {
number = input.nextInt();
//If number < 0 OR number > 1
if(number < 0 || number > 1) {
//The rest of the try-block will not be executed.
//Instead, the following catch-block will be executed.
throw new InputMismatchException();
}
break;
}
catch(InputMismatchException e) {
System.out.println("Enter 0=yes or 1=no");
//Clears the scanner to wait for the next number
//This is needed if the user enters a string instead of a number
input.nextLine();
}
If you don't know about try-catch-statements yet, I suggest to read this explanation. For details about the InputMismatchException, please see the documentation.
The problem now is that the user only has one chance to enter 0 or 1. If the user makes a wrong input the program will just stop. One solution to this problem is to just put the code in a while-loop:
int number;
while(true) {
try {
number = input.nextInt();
if(number < 0 || number > 1) {
throw new InputMismatchException();
}
break;
}
catch(InputMismatchException e) {
System.out.println("Enter 0=yes or 1=no");
input.nextLine();
}
}
After this block, we can be sure that number is either 0 or 1. So now we can add a simple if-statement to check the value:
if(number == 0) {
new Guess().doGuess();
}
return;
So all in all the code looks like this:
System.out.println("Do you want to play again? (enter 0 for yes and 1 for no): ");
int number;
while(true) {
try {
number = input.nextInt();
if(number < 0 || number > 1) {
throw new InputMismatchException();
}
break;
}
catch(InputMismatchException e) {
System.out.println("Enter 0=yes or 1=no");
input.nextLine();
}
}
if(number == 0) {
new Guess().doGuess();
}
return;
Don't forget to add the following import-statements:
import java.util.Scanner;
import java.util.InputMismatchException;
import java.util.Random;

Try this. Basically, if the user responds with "yes" , we will call the function again.
if (tries > 9) {
System.out.println("You should be able to do better!"
+ " You have hit your ten guess limit. The number" + " was: " + answer);
System.out.println("Do you want to play again? (yes/no): "); // modified line
if("yes".equalsIgnoreCase(input.next())){ // newly added if block
answer = generateRandomNumber();
tries=0;
i=0;
win = false;
doGuess();
}
return;
}

While loop is not looping back to the start with a new input from the user

I have been trying to perfect this program on my own, and I just can't see what I'm doing wrong. The aim of this program is to do these things.
1) ask user for number
2) if the number is positive, print out the number
3) if the number is also a prime number, print that it's also a prime number
4) keep doing the above things until a negative number is inputed by the user.
The problem is, the program only works and determines if a number entered is a prime number or not, at the beginning. After that, when the user is asked for another number (if it's greater than 0), the program just doesn't loop back to the beginning to determine if the number is prime. Instead, it just sticks to what the value at the beginning was determined to be (prime or not prime) and prints out the same statement as what you would get for the first value, for the second. I want it to reevaluate the value every time to see if the number is prime or not, until the user inputs a negative number.
P.S. This is my first year going for a C.S degree. I find programing really fun and challenging (the concept). But I embrace it that challenge and find a sense of accomplishment every time I work through these problems.
import java.util.Scanner;
public class Prime3 {
public static void main(String[] args) {
int userNum;
int i = 2;
boolean isPrime = true;
Scanner input = new Scanner(System.in);
// Ask user for initial number
System.out.println("Please enter a number.");
userNum = input.nextInt();
// Determining whether or not number entered is prime
while (i <= userNum/2) {
System.out.println("Checking if " + i + " is a multiple of n");
if (userNum%i == 0) {
System.out.println(i + " is a multiple of " + userNum);
isPrime = false;
break;
}
i++;
}
// Print out user number if the number is positive.
while (userNum > 0) {
System.out.println("You entered the number, " + userNum);
if (isPrime) { // If it's a prime, state that it's a prime
System.out.println("No even multiples found. " + userNum + " is a prime number");
}
userNum = input.nextInt();
}
System.out.println("Invalid input. Program now ending.");
System.exit(0);
}
}

Well, I see the problem. You should move while (userNum > 0) to the top. So your final code should look something like this:
public class Prime3 {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
// Ask user for initial number
System.out.println("Please enter a number.");
int userNum = input.nextInt();
while (userNum > 0) {
int i = 2;
boolean isPrime = true;
// Determining whether or not number entered is prime
while (i <= userNum / 2) {
System.out.println("Checking if " + i + " is a multiple of n");
if (userNum % i == 0) {
System.out.println(i + " is a multiple of " + userNum);
isPrime = false;
break;
}
i++;
}
// Print out user number if the number is positive.
System.out.println("You entered the number, " + userNum);
if (isPrime) { // If it's a prime, state that it's a prime
System.out.println("No even multiples found. " + userNum + " is a prime number");
}
userNum = input.nextInt();
}
System.out.println("Invalid input. Program now ending.");
System.exit(0);
}

In general construction of this code is error prone. You should do something like:
set userNum = 0
enter while (userNum >=0)
Call method which check if userNum is positive, if yes print
Call method which check if userNum is prime, if yes print
get new value from input console into userNum
end body of loop.
If you follow there should be no problem.

Last questions: Mastermind Java program

I have two questions regarding my code.
Why does is the output "Oops please enter a number between 1 and 6" when I enter a number between 1 and 6. When I try to be more specific and make an else if statement, nothing happens when I enter a number NOT between 1 and 6.
How do I restart my program? In my code, there is an if statement
when the user inputs "play again" My commented out line reads
Mastermind.main() to re run the program, but that didn't work.
Here is the code:
import java.util.Scanner;
public class Mastermind {
public static void main (String [] args) {
// boolean variable to signal when the game is over.
boolean done = false;
// Scanner object
Scanner scanner = new Scanner(System.in);
// sets the value to twelve outside the loop so it doesn't set back each time.
int guesses = 12;
System.out.println("Please enter a number between 1-6 to begin (or \"quit\") to exit.");
// while loop for the game
while (!done) {
//System.out.println("Please enter a number between 1-6 (or \"quit\") to exit the game:");
// user input
String input = scanner.nextLine();
int number = 0; //Just initialized to some number
// checks to see if the user wants to quit the game.
if (input.equalsIgnoreCase("quit")) {
System.out.println("Goodbye!");
done = true;
scanner.close();
}
else{
try{
//Trying to see if the input was a number
number = Integer.parseInt(input);
}
catch(Exception e){
//The input wasn't an integer, it's invalid the starts loop again.
System.out.println("Invalid input.");
continue;
}
}
// defines necessary int variables
int random1 = (int) (Math.random() * 7);
int random2 = (int) (Math.random() * 7);
int random3 = (int) (Math.random() * 7);
int random4 = (int) (Math.random() * 7);
// If the user doesn't and decides to play, it runs this code.
// checks to see if the user enters a number between 1-6
if (number >= 1 && number <= 6) {
if (number == random1) {
System.out.println("You guessed a correct number!");
guesses--;
System.out.println("guesses = " + guesses);
}
else if (number == random2) {
System.out.println("You guessed a correct number!");
guesses--;
System.out.println("guesses = " + guesses);
}
else if (number == random3) {
System.out.println("You guessed a correct number!");
guesses--;
System.out.println("guesses = " + guesses);
}
else if (number == random4) {
System.out.println("You guessed a correct number!");
guesses--;
System.out.println("guesses = " + guesses);
}
else {
System.out.println("Sorry that's not one of the numbers! Try again.");
guesses--;
System.out.println("guesses = " + guesses);
}
}
if (guesses == 0){
System.out.println("You've run out of guesses. To play again, enter \"play again\". Otherwise, enter or \"quit\")");
if (input.equalsIgnoreCase("play again")){
// how do I restart the program?
//Mastermind.main(); // QUESTION 2
}
else if (input.equalsIgnoreCase("quit")){
System.out.println("Goodbye!");
done = true;
scanner.close();
}
else {
System.out.println("Goodbye!");
done = true;
scanner.close();
}
}
else { //QUESTION 1
System.out.println("Oops! Please choose a number between 1 and 6");
}
}
}
}

You're printing that message every time through the loop whenever guesses == 0 evaluates to false. You probably just need to switch the order of the two blocks. Instead of this:
if (number >= 1 && number <= 6) {
...
}
if (guesses == 0) {
...
}
else { //QUESTION 1
System.out.println("Oops! Please choose a number between 1 and 6");
}
Use this:
if (number >= 1 && number <= 6) {
...
}
else { //QUESTION 1
System.out.println("Oops! Please choose a number between 1 and 6");
}
if (guesses == 0) {
...
}
Regarding restarting your program: if I'm reading the logic correctly, all you need to do is keep done set to false and reset guesses to 12.
Two other logic points. First, you should probably either continue or break after detecting that the user has entered "quit". Second, it seems like you are generating four new random integers for every user guess. I don't know if that's what you intended, but you might want to change the logic a bit. That might also affect the restart logic.

How would I add "You got it right in ... guesses!"

I need to add "You got it right in ... guesses!" but I'm not exactly sure how. Can someone please explain to me how to do this in java?
I would like it to display a println at the end saying how many tries it took for the user to get the number correct.
import java.util.*;
public class prog210c
{
public static void main()
{
Scanner sc = new Scanner(System.in);
Random rn = new Random();
int randomNum = rn.nextInt(90) + 10;
System.out.println("I am thinking of a number between 1 and 100");
while (true) {
System.out.print("What do you think it is? ");
int guess = sc.nextInt();
if(guess < randomNum)
{
System.out.println("Higher--Try Again");
}
else if(guess > randomNum)
{
System.out.println("Lower--Try Again");
}
else if(guess == randomNum)
{
System.out.println("Correct!");
break;
}
else
{
System.out.println("Enter a number between 1 and 100");
}
}
//System.out.println("You got it right in " + + " guesses");
} //end main
} //end class

Just create some int variable to store your number of attempts in and increment it every time you read in a guess.
int attempts = 0;
System.out.println("I am thinking of a number between 1 and 100");
while (true) {
System.out.print("What do you think it is? ");
int guess = sc.nextInt();
attempts++;
/**
* The rest of your loop code here.
*/
}
System.out.println("You got it right in " + attempts + " guesses");

The simplest way to do this is declared a counter integer, and in your logic increment it every time the user attempts.
int guessCounter = 0;
while(true) // Also do not use an infinite while loop, have an expression that can be terminated
{
...obtain input
if(guess < randomNum)
{
...
guessCounter++;
}
else if (guess > randomNum){
....
guessCounter++;
}
System.Out.println("The number of attempts " + guessCounter);
}

You could do this by creating a variable to store the number of tries, like an int, and then add one to the int every time the user guesses, by using variable++:
public static void main(){
Scanner sc = new Scanner(System.in);
Random rn = new Random();
int tries = 0;
int randomNum = rn.nextInt(90) + 10;
System.out.println("I am thinking of a number between 1 and 100");
while(true){
System.out.print("What do you think it is? ");
int guess = sc.nextInt();
//Rest of your code here
}
System.out.println("You got it right in " + tries + " guesses");
}
and if you want to go even above and beyond, you could make it so it says You got it right in 1 guess instead of it saying You got it right in 1 guesses, if the user gets the number correct on their first try. We can do this by using the ternary Java operator, which is pretty much a compact if-statement:
String s = (tries == 1 ? "guess" : "guesses");
What this is pretty much doing is: if this is true ? do this : else do this
Now we can change the You got it right in... part of your program to say guess instead of guesses if the user guesses the number on their first try:
String s = (tries == 1 ? "guess" : "guesses");
System.out.println("You got it right in " + tries + "" + s);

While loop bugs

Hello I am a beginner Java programmer. My Program keeps ending when I put the correct number in (with out printing the message ), or it wont go from a lower number to a higher one with out ending?
Can someone tell me what I am doing wrong?
package week3;
import java.util.Scanner;
public class Week3 {
public static void main(String[] args) {
Scanner In = new Scanner(System.in);
int Guess ;
int count = 0;
count++;
int c = 55;
System.out.println("Welcome to the Higher / Lower game! Try to guess the"
+ "number between 1 and 100. ");
System.out.print("Enter your guess: ");
Guess = In.nextInt();
if(Guess == c)
{
System.out.println("The number was 55 you guessed correctly! "
+ " it took you " + count +" tries");
}//end if
while (Guess < 1)
{
System.out.println("Sorry, the guess needs to be a number between 1 and"
+ " 100. Please try again:");
Guess = In.nextInt();
}//End while < 1
while (Guess > 100)
{
System.out.println("Sorry, the guess needs to be a number between 1 and"
+ " 100. Please try again:");
Guess = In.nextInt();
}//end while <100
while (Guess >= 56)
{
System.out.println("The number is lower.");
Guess = In.nextInt();
} //end while over 55
while (Guess <= 54)
{
System.out.println("The number is higher.");
Guess = In.nextInt();
}//end while lower than 55
}//end main
}//end class

I can see the problem, but you would be better off trying to find it yourself. (Or having another go ...)
Hints:
Try hand-executing the code. Pretend you are the computer, and use a pencil and paper to simulate what it would do.
Have you tried using a debugger?
Some of the comments are good hints too.
While I have your ear, you also should pay attention to your programming style. And one universal style rule for Java is that variables should start with a lower-case letter. Your In and Guess variables violate this.

System.out.println("Welcome to the Higher / Lower game! Try to guess the"
+ "number between 1 and 100. ");
while (true) {
System.out.print("Enter your guess: ");
Guess = Integer.parseint(In.nextLine());
if(Guess == c)
{
System.out.println("The number was 55 you guessed correctly! "
+ " it took you " + count +" tries");
break;
}
if (Guess < 1)
{
System.out.println("Sorry, the guess needs to be a number between 1 and"
+ " 100. Please try again:");
}
if (Guess > 100)
{
System.out.println("Sorry, the guess needs to be a number between 1 and"
+ " 100. Please try again:");
}
if (Guess >= 56)
{
System.out.println("The number is lower.");
}
if (Guess <= 54)
{
System.out.println("The number is higher.");
}
}
}
}
Hopefully this gives you the idea of using the while loop.

The structure of your program is incorrect.
You only need one while loop. Begin your program with a while loop, and continue with conditions, such that:
boolean numFound = false;
while (!numFound) {
//conditions
}