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Troubleshooting Character Array Problem in Java [closed]

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I was going through a Palindrome( Specifically String Palindrome) Problem and was checking whether the string is palindrome or not. But a problem struck in the program
public static void main(String args[])
{
Scanner sc= new Scanner(System.in);
int n,flag=0;
n=sc.nextInt();
char a[]=new char[n];
int l=0;
int h=n-1;
while(l<h)
{
if(a[l++]!=a[h--])
{
flag=1;
}
}
if(flag==1)
{
System.out.println("String is not Palindrome");
}
else{
System.out.println("String is Palindrome");
}
}
So above is the code which I wrote but the problem is, I have created a character array instead of the string.
The main point of the argument is the above code correct in terms of code standards.

is the above code correct in terms of code standards
Not really:
Don't name a local variable l (lowercase L). It is too easy to confuse with 1 (one).
Since I don't know what h is supposed to be a shorthand for, I changed l and h to i and j below, as those are very common integer iterator variable names.
Don't declare a local variable before it's needed. Use int n = sc.nextInt();
Don't put array declaration on the variable name. Put it on the type, since it defines the type.
Don't use 0 / 1 for false / true values. Change flag to a boolean, and name it better, e.g. describe its value. notPalindrome seems appropriate here. It helps document the code.
The while loop should be a for loop. It helps keeping loop logic together, and isolated from other logic, and it helps limit the scope of the loop variable(s).
Those were my comments related to coding standards.
However, your code doesn't work, because you never get a string from the user. Your choice of using char[] is fine, but you need to change the logic for getting it. See code below for how to use toCharArray() to do that.
Also, once a difference is found, you should exit the loop, either by also checking the boolean variable in the loop condition, or by using break. Personally, I prefer break.
Scanner sc = new Scanner(System.in);
String sentence = sc.nextLine();
char[] a = sentence.toCharArray();
boolean notPalindrome = false;
for (int i = 0, j = a.length - 1; i < j; i++, j--) {
if (a[i] != a[j]) {
notPalindrome = true;
break;
}
}
if (notPalindrome) {
System.out.println("String is not Palindrome");
} else {
System.out.println("String is Palindrome");
}

please use below code to check given String/number Palindrome or Not
public static void main(String args[]) {
String original, reverse = "";
Scanner in = new Scanner(System.in);
System.out.println("Enter String ");
original = in.nextLine();
int n = original.length();
for ( int index = n - 1; index >= 0; index-- ) {
reverse = reverse + original.charAt(index);
}
if (original.equals(reverse)) {
System.out.println("String is Palindrome");
} else {
System.out.println("String is not Palindrome");
}
}

Creating a random output from an user input array [closed]

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public class decisionMaker {
public static void main(String args[]) {
String option[] = new String[10];
// Output
for (int i = 0; i <= 9; i++) {
Scanner input = new Scanner(System.in);
System.out.print("Enter the next option:");
option[i] = input.next();
System.out.println(" ");
}
for (int i = 0; i <= 9; i++) {
System.out.println("option: ");
System.out.println("option[i]+" ");
}
// Output
}
I'm trying to figure out how to add a count to the options, exit and end the program after entering a certain letter or number, and how to create a random output from the user input. I want it to give me one option that I had input at random. Can anyone help me with one or a few of these things. I'm trying to learn to code on my own, and I'm stuck on these.

Randomness
You can generate random numbers using java.util.Random;:
import java.util.Random;
public class SomeClass{
static Random rand = new Random();
public static void main(String args[]){
System.out.println(rand.nextInt());
}
}
About some broken code:
If you want to print out the value of a variable with System.out.println() then you need only type the variable without any quotation marks. The code you've written below will not compile:
System.out.println("option: ");
System.out.println("option[i]+" ");
Assuming that's what you want to do, it should instead be written as:
System.out.println("option: ");
System.out.println(option[i]);
Or even System.out.println("option: \n"+option[i]);
(The escape sequence \n when placed inside of quotation marks just indicates to the console to add a new line.)
Scanner:
Additionally, as nick zoum pointed out, your Scanner object should be initialized outside of the for loop, such as right underneath of the main() method.
Please comment below if you need clarification or if I misunderstood what you were looking for. It was very hard to understand your question.

You could try something like this:
public class DecisionMaker {
public static void main(String[] args) {
// output
Scanner scanner = new Scanner(System.in);
int size = getInt(scanner);
String option[] = new String[size];
for (int index = 0; index < size; index++) {
System.out.print("Enter the next option:");
option[index] = scanner.next();
}
int index = (int) (Math.random() * size);
System.out.println(option[index]);
scanner.close();
// output
}
public static int getInt(Scanner scanner) {
int size = 0;
while (size <= 0) {
if (scanner.hasNext()) {
if (scanner.hasNextInt()) {
size = scanner.nextInt();
}
}
if (size <= 0) {
System.out.println("The input: " + scanner.next() + " is not a valid value.");
}
}
return size;
}
}
How the program works:
The Scanner is initialized in the beginning and there is only
one instance of it.
Then the program will wait until the user inserts a valid number for
the size of options.
The next 5 lines were essentially copied from your code.
Finally we get a random Integer in the range of 0 - (size - 1) and print
the String of the array with that index.

Not able to take user input when using while loop [closed]

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I have this code bellow which is supposed to take a user input and store it in an array, and I was just wondering why it is not allowing me to input any numbers.
Should the input part be inside the if statement? Also what is the best way to make it work properly?
import java.util.*;
public class fun_with_loops {
static Scanner scan = new Scanner(System.in);
public static void main (String[] args) throws java.io.IOException
{
int[] numbers = new int[10];
int numberSize = 0;
System.out.print("Enter a few numbers please\n");
while (numbers.length < 10)
{
int input = scan.nextInt();
if (input != 0)
{
numbers[numberSize] = input;
numberSize++;
}
else
{
break;
}
}
}
}

Problem
The following expression on loop's control is always evaluated as false:
while (numbers.length < 10)
since array's length is in fact equals 10 as when declared.
Solution
In order to program work as expected you have to use numberSize variable as control:
while (numberSize < 10)
since it grows based on number of inputs.

As Am_I_Helpful stated, you are using a while loop on a value that will not change. I am not sure if the use while is needed in this case. Since you want to loop a specific amount of times you might want to use a for loop. If the amount of times will depend on the size of your array, you could still replace the "10" by your array length (numbers.length).
for (int i; i< 10; i++)
{
int input = scan.nextInt();
if (input != 0)
{
numbers[numberSize] = input;
numberSize++;
}
else
{
break;
}
}
Hoping it helped!
Dan
a short and sweet summary of when to use each loop:
http://mathbits.com/MathBits/CompSci/looping/whichloop.htm
but of course it always depends of your goal while coding so it's sometimes hard to say which is best if you are not the one coding.

Because the array is initialized to size 10, the length will always be 10. A counter variable needs to be used. Here is the code:
static Scanner scan = new Scanner(System.in);
public static void main (String[] args) throws java.io.IOException
{
int[] numbers = new int[10];
System.out.print("Enter a few numbers please\n");
int count = 0;
while (count < 10)
{
int input = scan.nextInt();
if (input != 0)
{
numbers[count] = input;
count++;
}
else
{
break;
}
}

The length property returns the size of the array, not the number of elements that are present in the array. You need to keep track of number of elements in the array on your own.
for(int eleCount = 0; eleCount < 10; eleCount++)
{
int input = scan.nextInt();
if (input != 0)
{
numbers[eleCount] = input;
}
else
{
break;
}
}

To Add all prime digits present in a number in java. what's error in this code? [closed]

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public static void main(String args[]){
Scanner sc = new Scanner(System.in) ;
System.out.print("Enter String: ");
String str = sc.nextLine();
int n=str.length();
int count=0;
char[] strArray = str.toCharArray();
for(int i=0;i<n;i++)
{
if(isPrime(strArray[i]))
{
count=count+strArray[i];
}
}
System.out.println (count);
}
private static boolean isPrime(int num)
{
if(num==1 ||(num!=2 && num%2==0))
{
return false;
}
else
{
for(int i=2;i<num/2;i++)
{
if(num%i==0)
return false;
}
}
return true;
}
I'm converting string to character array to check for prime and calling the function
It's not giving the correct output.
Input:
123
Output:
5
I'm not getting the error here. what's the error in this code?

When you pass strArray[i] to isPrime, if you are passing '3', you are not checking if the number 3 is prime, you are checking if the numeric value of the character '3' is prime.
Assuming your input contains only digits, try to change the code to :
for(int i=0;i<n;i++)
{
if(isPrime(strArray[i]-'0'))
{
count=count+strArray[i]-'0';
}
}

Why doesn't the following program work? [closed]

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I can't figure out why the following program doesn't work. Please help me where did I make a mistake. Thank you.
import java.util.Scanner;
public class LargestNumber {
public static void main(String[] args) {
int[] numbers = new int[100];
int largestNumber = 0;
System.out.println("Enter numbers. When you want to finish, type 'finish'.");
Scanner sc = new Scanner(System.in);
do {
if (sc.hasNextInt()) {
for (int counter = 0; counter < 10; counter++)
numbers[counter] = sc.nextInt();
}
if (!sc.hasNextInt() && !sc.hasNext("finish")) {
System.out.println("It's neither number nor 'finish'.");
}
}
while (!sc.hasNext("finish"));
for (int x : numbers) {
if (x > largestNumber) {
largestNumber = x;
}
}
System.out.println("The largest number is: " + largestNumber);
}
}

This part:
do {
if (sc.hasNextInt()) {
for (int counter = 0; counter < 10; counter++)
numbers[counter] = sc.nextInt();
}
if (!sc.hasNextInt() && !sc.hasNext("finish")) {
System.out.println("It's neither number nor 'finish'.");
}
}
while (!sc.hasNext("finish"));
makes no sense. You:
test if the next thing in the input is an integer;
attempt to parse ten next tokens, assuming that they are all integers;
at the eleventh token you check whether it's another integer or "finish";
throw an exception if it's neither;
repeat everything if it's not "finish".
What you should actually do is something much, much simpler:
check next token:
if it's "finish", you're done;
if it's an integer, parse it;
otherwise throw error;
repeat this for up to 100 times;
you are done accepting input. Proceed to processing it.

I think that Scanner is unnessecarily complicated and doesn't work to much of the time. Here's how to do it the old fashioned way:
public class LargestNumber {
public static void main(String[] args) {
int largestNumber=0;
System.out.println("Enter numbers. When you want to finish, type 'finish'.");
BufferedReader r = new BufferedReader(new InputStreamReader(System.in));
String line;
while (!(line = r.readLine()).equals("finish")) {
int val = Integer.parseInt(line);
if (val > largestNumber)
largestNumber = val;
}
System.out.println("The largest number is: " + largestNumber);
}
}
For this, enter each number on a new line. I used a shorter algorithm here, which is to read one number, and if it is bigger than the maximum so far, the new number is the maximum so far

According to the doc:
Throws:
InputMismatchException - if the next token does not match the Integer regular expression, or is out of range
So i thing you could do this instead:
int counter = 0;
while (counter < numbers.length) {
if (sc.hasNextInt()) {
numbers[counter++] = sc.nextInt();
} else {
if (sc.hasNext("finish")) {
sc.close();
break;
} else {
System.out.println("It's neither number nor 'finish'.");
sc.next();
}
}
}
for (int x : numbers) {
if (x > largestNumber) {
largestNumber = x;
}
}
System.out.println("The largest number is: " + largestNumber);
hope that helps