Develop Reference

Same input keeps adding to the arraylist

I'm writing a number guessing game in java.
Number guessing game is a numeric version of famous hangman, where computer picks a
number between a prespecified range and user has to guess that number.
Requirements:
User must guess a number between 0-1000 and tells the user the range of guessed
number.
User has max 10 guesses.
Every time user makes a guess, total guesses reduce by one.
Computer keeps track of all the numbers user has guessed so far and shows this
information before next guess.
If the guess is correct, game ends in a win. In case of incorrect guess, computer gives a
hint to the user. If the user guess is greater than the picked number, then client tell the
user that ‘your guess is bigger’ and in case of being smaller appropriate message is
shown.
In case of invalid guess (alphabets, symbols and repeated guesses) one warning is given
and on next warning user loses a guess
The following code is running fine but it always shows the same number after guesses number. I think its not adding the new input in the arrraylist rather the first one everytime.
import java.util.*;
import java.lang.*;
public class NumberGuess {
public static void main(String[] args) {
int tries = 10;
ArrayList<Integer> guessed = new ArrayList();
int warnings = 2;
int i = 0;
Random rand = new Random();
int random = rand.nextInt(1000);
private void StartMenu () {
System.out.println("\" Welcome to the Number guessing game!\n I am thinking of a number between 0-1000\n You have 1 warning.\n You have 1 warning.\n ------------ ");
}
public char[] ToCharacterArray (String input){
char arr[] = new char[input.length()];
arr = input.toCharArray();
return arr;
}
public boolean CheckInput ( char arr[]){
if (Character.isDigit(arr[0])) {
return true;
} else {
return false;
}
}
String input;
while (tries > 0 && warnings > 0) {
System.out.println("You have " + tries + " guesses left.");
if (tries == 10) {
System.out.println("guessed number: ");
} else {
System.out.println("guessed number: ");
for (Integer a : guessed) {
System.out.println(guessed.get(i));
}
}
System.out.println("Please guess a number:");
Scanner sc = new Scanner(System.in);
input = sc.next();
char InputString[] = ToCharacterArray(input);
if (CheckInput(InputString)) {
int intInput = Integer.parseInt(input);
guessed.add(intInput);
if (intInput > random) {
System.out.println("Your guess is greater");
}
if (intInput < random) {
System.out.println("Your guess is smaller");
}
if (intInput == random) {
System.out.println("Congrats! You win.");
System.out.println("The guessed number is: " + intInput);
tries = -1;
}
}
tries--;
}
}
}

The problem is because you iterate over the guessed numbers, and then print out the item of index i from that list. The number i at that point will always be zero, so it will always print just the first element from that list. Instead, you can just print the a, that is the element itself, after the iteration on guessed. Here is how it will look like:
System.out.println("guessed number: ");
for (Integer a : guessed) {
System.out.println(a);
}

Store user input in array multiple times

I'm working on a project which...
Allows the user to input 4 numbers that are then stored in an array for later use. I also want every time the user decided to continue the program, it creates a new array which can be compared to later to get the highest average, highest, and lowest values.
The code is not done and I know there are some things that still need some work. I just provided the whole code for reference.
I'm just looking for some direction on the arrays part.
*I believe I am supposed to be using a 2-D array but I'm confused on where to start. If I need to explain more please let me know. (I included as many comments in my code just in case.)
I tried converting the inputDigit(); method to accept a 2-D array but can't figure it out.
If this question has been answered before please redirect me to the appropriate link.
Thank you!
package littleproject;
import java.util.InputMismatchException;
import java.util.Scanner;
public class littleProject {
public static void main(String[] args) {
// Scanner designed to take user input
Scanner input = new Scanner(System.in);
// yesOrNo String keeps while loop running
String yesOrNo = "y";
while (yesOrNo.equalsIgnoreCase("y")) {
double[][] arrayStorage = inputDigit(input, "Enter a number: ");
System.out.println();
displayCurrentCycle();
System.out.println();
yesOrNo = askToContinue(input);
System.out.println();
displayAll();
System.out.println();
if (yesOrNo.equalsIgnoreCase("y") || yesOrNo.equalsIgnoreCase("n")) {
System.out.println("You have exited the program."
+ " \nThank you for your time.");
}
}
}
// This method gets doubles and stores then in a 4 spaced array
public static double[][] inputDigit(Scanner input, String prompt) {
// Creates a 4 spaced array
double array[][] = new double[arrayNum][4];
for (int counterWhole = 0; counterWhole < array.length; counterWhole++){
// For loop that stores each input by user
for (int counter = 0; counter < array.length; counter++) {
System.out.print(prompt);
// Try/catch that executes max and min restriction and catches
// a InputMismatchException while returning the array
try {
array[counter] = input.nextDouble();
if (array[counter] <= 1000){
System.out.println("Next...");
} else if (array[counter] >= -100){
System.out.println("Next...");
} else {
System.out.println("Error!\nEnter a number greater or equal to -100 and"
+ "less or equal to 1000.");
}
} catch (InputMismatchException e){
System.out.println("Error! Please enter a digit.");
counter--; // This is designed to backup the counter so the correct variable can be input into the array
input.next();
}
}
}
return array;
}
// This will display the current cycle of numbers and format all the data
// and display it appropriatly
public static void displayCurrentCycle() {
int averageValue = 23; // Filler Variables to make sure code was printing
int highestValue = 23;
int lowestValue = 23;
System.out.println(\n--------------------------------"
+ "\nAverage - " + averageValue
+ "\nHighest - " + highestValue
+ "\nLowest - " + lowestValue);
}
public static void displayAll() {
int fullAverageValue = 12; // Filler Variables to make sure code was printing
int fullHighestValue = 12;
int fullLowestValue = 12;
System.out.println(" RESULTS FOR ALL NUMBER CYCLES"
+ "\n--------------------------------"
+ "\nAverage Value - " + fullAverageValue
+ "\nHighest Value - " + fullHighestValue
+ "\nLowest Value - " + fullLowestValue);
}
// This is a basic askToContinue question for the user to decide
public static String askToContinue(Scanner input) {
boolean loop = true;
String choice;
System.out.print("Continue? (y/n): ");
do {
choice = input.next();
if (choice.equalsIgnoreCase("y") || choice.equalsIgnoreCase("n")) {
System.out.println();
System.out.println("Final results are listed below.");
loop = false;
} else {
System.out.print("Please type 'Y' or 'N': ");
}
} while (loop);
return choice;
}
}

As far as is understood, your program asks the user to input four digits. This process may repeat and you want to have access to all entered numbers. You're just asking how you may store these.
I would store each set of entered numbers as an array of size four.
Each of those arrays is then added to one list of arrays.
A list of arrays in contrast to a two-dimensional array provides the flexibility to dynamically add new arrays.
We store the digits that the user inputs in array of size 4:
public double[] askForFourDigits() {
double[] userInput = new double[4];
for (int i = 0; i < userInput.length; i++) {
userInput[i] = /* ask the user for a digit*/;
}
return userInput;
}
You'll add all each of these arrays to one list of arrays:
public static void main(String[] args) {
// We will add all user inputs (repesented as array of size 4) to this list.
List<double[]> allNumbers = new ArrayList<>();
do {
double[] numbers = askForFourDigits();
allNumbers.add(numbers);
displayCurrentCycle(numbers);
displayAll(allNumbers);
} while(/* hey user, do you want to continue */);
}
You can now use the list to compute statistics for numbers entered during all cycles:
public static void displayAll(List<double[]> allNumbers) {
int maximum = 0;
for (double[] numbers : allNumbers) {
for (double number : numbers) {
maximum = Math.max(maximum, number);
}
}
System.out.println("The greatest ever entered number is " + maximum);
}

Parsing a String to an Integer

So my biggest problem is that I cannot seem to remember how to parse a string into an int so that I can idiot proof my code. My goal here is to find out if the user enters in a word instead of an int and then I can explain to them what an integer is. Can someone please help? I just need a simple list of parsing commands so that I can study them for use in the future, once there is a simple list I think I'll be able to figure all the others out from there.
import java.util.Scanner;
import java.util.*;
public class SelfTestNumberNine
{
public static void main(String[] args)
{
boolean test = false;
int num = 0;
int sum = 0;
int count = 0;
int pos = 0;
int neg = 0;
Scanner in = new Scanner(System.in);
while(!test)
{
num = 0;
System.out.print("Enter in an Integer Value: ");
String letta = in.next();
if(??parsing stuff goes here!!)
{
num = in.nextInt();
count++;
if(num > 0)
{
pos++;
sum = sum + num;
}
else if(num < 0)
{
neg++;
sum = num + sum;
}
else
{
test = true;
}
}
else
{
System.out.println("An Integer is a number that is positive or
negative,\nand does not include a decimal point.");
}
}//end while
System.out.println("Total: " + sum);
double avg = sum / count;
System.out.println("Average: " + avg);
}//end main
}//end class
Basically, the program asks the user to input integers, counts the number of positive and negatives, and prints out the total and average (Ignoring 0). The program ends when the user inputs a 0.
P.S. Thanks for your time!! ]:-)

If you want to ensure that the user has entered an int without throwing an exception if they don't you can use the hasNextInt() method:
System.out.println("Enter an int (0) to quit");
//While the user has not entered a valid int
while (!input.hasNextInt()) {
System.out.println("Please enter an integer: ");
//Consume the bad input
input.nextLine();
}
Which will loop until they enter a valid int. A sample run (- denotes user input):
Enter an int (0 to quit)
-No
Please enter an integer:
-Never!!
Please enter an integer:
-Ok ok fine
Please enter an integer:
-3

You can do this in two ways.
- Integer.parseInt()
- Integer.valueOf()
String myStr = "1";
int parsedInt = Integer.parseInt(myStr);
int valueOf = Integer.valueOf(myStr);
System.out.println("Parse Int: " + parsedInt);
System.out.println("Value Of: " + valueOf);
Note: You might get exception if the input is not parseable. NumberFormatException.

You can use a Boolean method and a try-catch to check if you can parse the string to an Integer.
public static boolean isInteger(String s) {
try {
Integer.parseInt(s);
} catch(NumberFormatException e) {
return false;
} catch(NullPointerException e) {
return false;
}
// only got here if we didn't return false
return true;
}

Number comparision in java [duplicate]

This question already has answers here:
How do I check if a number is a palindrome?
(53 answers)
Closed 5 years ago.
This might be a very dumb question. I tried to reverse the input number and compare it.If they are same then, the output should be "the number entered is a palindrome" But, I'm getting out for every number like it is a palindrome.
package com.practise.examples;
import java.util.Scanner;
public class Practise
{
public static void main(String[] args) {
Scanner s=new Scanner(System.in);
System.out.println("enter the number to reverse it:\n");
int num=s.nextInt();
int revNum=0;
while(num!=0)
{
revNum=revNum *10;
revNum= revNum+ num%10;
num=num/10;
}
System.out.println("the reverse of the number is: " +revNum);
if(revNum==num)
{
System.out.println("the number is a palindrome" );
}
else
{
System.out.println("the number entered is not a palindrome");
}
}
}

Easier way:
String num=Integer.toString(s.nextInt());
String revNum = new StringBuffer(num).reverse().toString();
System.out.println("the reverse of the number is: " +revNum);
if(revNum.equals(num))
System.out.println("the number is a palindrome" );
else
System.out.println("the number entered is not a palindrome");
If you're insisting on your method:
Scanner s=new Scanner(System.in);
System.out.println("enter the number to reverse it:\n");
int num=s.nextInt();
int original = num;
int revNum=0;
while(num!=0)
{
revNum=revNum *10;
revNum= revNum+ num%10;
num=num/10;
}
System.out.println("the reverse of the number is: " +revNum);
if(revNum==original)
{
System.out.println("the number is a palindrome" );
}
else
{
System.out.println("the number entered is not a palindrome");
}
}

Try something like this:
public static int reverse(int num)
{
try
{
return Integer.parseInt(new StringBuilder(String.valueOf(num)).reverse().toString());
}
catch (Exception ex)
{
// Should not happen...
}
}

You have modified num for getting the reverse, and then using the same num for comparison. Use temporary variables.

your idea seems to only work in VERY specific instances, and the code itself... well, ill just give you a different idea.
create a stack and a queue.
take the original input, and add each consecutive item to each the stack and the queue.
once the queue and stack are full...
iterate until length=0
if stack.pop != queue.dequeue
palindrome=false

you can cast your number to a string and check doe's its palindrome?
import java.util.Scanner;
public class Main{
public static void main(String[] args) {
Scanner s=new Scanner(System.in);
System.out.println("enter the number to reverse it:\n");
int num=s.nextInt();
if (isPalindrome(num+"")){
System.out.println("the number is a palindrome" );
}else{
System.out.println("the number entered is not a palindrome");
}
}
public static boolean isPalindrome(String s) {
int n = s.length();
for (int i = 0; i < (n/2); ++i) {
if (s.charAt(i) != s.charAt(n - i - 1)) {
return false;
}
}
return true;
}
}

Arrays with user input

I am trying to write a program that repeatedly asks the user to supply scores (out of 10) on a test.It needs to continue until a negative value is supplied. Values higher than 10 should be ignored. I also calculated the average of the inputs. After the scores have been inputted, i need to use a single array to produce a table that automatically fills the test scores and the number of occurrences of the certain test score.
I wanted it to look something like this:
Score | # of Occurrences
0 3
1 2
2 4
3 5
4 6
and so on.. P
I am a beginner and this is my first question, so i am sorry if i made a mistake in posting the question or something.
import java.io.*;
import java.util.*;
public class Tester1
{
public static void main()
{
Scanner kbReader= new Scanner (System.in);
int score[] = new int [10];//idk what im doing with these two arrays
int numofOcc []= new int [10];
int counter=0;
int sum=0;
for (int i=0;i<10;i++)// Instead of i<10... how would i make it so that it continues until a negative value is entered.
{
System.out.println("Enter score out of 10");
int input=kbReader.nextInt();
if (input>10)
{
System.out.println("Score must be out of 10");
}
else if (input<0)
{
System.out.println("Score must be out of 10");
break;
}
else
{
counter++;
sum+=input;
}
}
System.out.println("The mean score is " +(sum/counter));
}
}

You could use a do...while loop like this:
import java.io.*;
import java.util.*;
public class Tester1
{
public static void main(String args[]) {
Scanner kbReader= new Scanner (System.in);
int scores[] = new int [10];
int counter = 0;
int sum = 0;
int input = 0;
do {
System.out.println("Enter score out of 10 or negative to break.");
input=kbReader.nextInt();
if (input<0) {
break;
} else if (input>10) {
System.out.println("Score must be out of 10");
} else {
scores[input]++;
counter++;
sum+=input;
}
} while (input>0);
System.out.println("Score\t# of occur...");
for(int i =0; i<10; i++) {
System.out.println(i + "\t" + scores[i]);
};
System.out.println("The mean score is " +(sum/counter));
}
}
The formatting can certainly be done better (without c-style tabs) but I don't remember the syntax at the moment.

I think what you need is a List Array! Create ArrayList from array
Think of it as a dynamic array, you don't need to specify the size of the array and it is expanded/made smaller automatically.

What you're missing is a while loop. Here is a nice way to loop through a Scanner for input. It also catches numbers greater than 10 and provides an error message:
public static void main() {
Scanner s = new Scanner(System.in);
ArrayList<Integer> list = new ArrayList<Integer>();
int response = 0;
while (response >= 0) {
System.out.print("Enter score out of 10: ");
response = s.nextInt();
if (response > 10) {
System.out.println("Score must be out of 10.");
} else if (response >= 0) {
list.add(response);
}
}
// Do something with list
}