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Reverse integer including 0's in java

I have to do a program that returns the reverse of a number that is input by a user, event the numbers that start and finish with 0 (ex. 00040, it would print 04000)
I was able to do the reverse of the number, but it doesn't print out the 0's and I can't use String variables, just long variables or integers.
Here is my code:
import java.util.Scanner;
public class Assignment_2_Question_2 {
public static void main(String[] args) {
Scanner keyboard = new Scanner (System.in);
System.out.println("Welcome to Our Reversing Number Program");
System.out.println("-----------------------------------------");
System.out.println();
System.out.println("Enter a number with at most 10 digits:");
long number = keyboard.nextInt();
long nbDigits = String.valueOf(number).length();
System.out.println("Number of digits is " + nbDigits);
System.out.print("Reverse of " + number + " is ");
long revNumber = 0;
while (number > 0){
long digit = number % 10;
if (digit == 0){ // The teacher told me to add this
nb0 ++; // need to not take into account the 0's inside the number
}
revNumber = revNumber * 10 + digit;
number = number/10;
}
for (int i = 0; i < nb0; i++) { // This will print the number of 0's counted by the if statement and print them out.
System.out.println("0");
}
System.out.println(revNumber);
String answer;
do{
System.out.println("Do you want to try another number? (yes to repeat, no to stop)");
answer = keyboard.next();
if (answer.equalsIgnoreCase("yes")){
System.out.println("Enter a number with at most 10 digits:");
long otherNumber = keyboard.nextInt();
long nbrDigits = String.valueOf(otherNumber).length();
System.out.println("Number of digits is " + nbrDigits);
System.out.print("Reverse of " + otherNumber + " is ");
long reversedNumber = 0;
while (otherNumber != 0){
reversedNumber = reversedNumber * 10 + otherNumber%10;
otherNumber = otherNumber/10;
}
System.out.println(reversedNumber);
}
else
System.out.println("Thanks and have a great day!");
}while(answer.equalsIgnoreCase("yes")&& !answer.equalsIgnoreCase("no"));
}
}
Can someone help me? Thank you

Probably not what is intended but clearly (based on problem statement) you must see all digits entered (to include leading 0's) otherwise it is an "impossible solution" - and you state you cannot receive input as a String...
So this snippet reads one digit at a time where each digit is received as an int:
Scanner reader = new Scanner(System.in);
reader.useDelimiter(""); // empty string
System.out.print("Enter number: ");
while (!reader.hasNextInt()) reader.next();
int aDigit;
int cnt = 0;
while (reader.hasNextInt()) {
aDigit = reader.nextInt();
System.out.println("digit("+ ++cnt + ") "+aDigit);
}
System.out.println("Done");
Prints (assume user enter 012 (enter)):
Enter number: digit(1) 0
digit(2) 1
digit(3) 2
Done
You naturally have more work to do with this but at least you have all user entered digits (including leading zeros).

You can use buffer reader;
Like this given code And if you want to do some arithmetic operations in the numbers then you can convert it into int using parseInt method.:-
import java.util.Scanner;
import java.lang.*;
class Main {
public static void main(String args[])
{
System.out.println("ENTER NUM");
Scanner SC = new Scanner(System.in);
String INP = SC.nextLine();
StringBuffer SB = new StringBuffer(INP);
SB.reverse() ;
System.out.println(SB);
}
}

trying to learn how to error check my code

I'm trying to ask the user for two two-digit numbers and then perform a length check and a type check on both of the numbers, then I want to output the sum of the numbers. Here's what I have so far:
package codething;
import java.util.Scanner;
public class Practice {
public static void main(String[] args) {
Scanner number = new Scanner(System.in); // Reading from System.in
System.out.println("Enter a two digit number (10-99) ");
int n = number.nextInt();
if(number.hasNextInt()) {
} else {
System.out.println("Error");
}
int m;
int length = String.valueOf(number).length();
if (length == 2) {
} else {
System.out.println("this isnt a valid input and you have killed my program ;(");
}
Scanner number1 = new Scanner(System.in);
System.out.println("Enter another two digit number (10-99) ");
m = number.nextInt();
if(number1.hasNextInt()) {
m = number1.nextInt();
} else {
System.out.println("Error");
}
int sum = n + m;
System.out.println(sum);
}
}
At the moment my program won't even ask me for my second input. Not sure what to do :/

So several things:
-Don't construct more than one Scanner objects to read from System.in. It just causes problems.
-You're using String.valueOf() to convert an int to a String. It is better to simply check to make sure it is between 10 and 99.
-You check to make sure that the Scanner has a next int after you call nextInt which won't help. You need to make sure that there is a next int.
-A lot of your if statements have an empty if block and then you do something in the else. You can just do the opposite in the if and omit the else (Instead of if(length ==2) {} you can do if(length != 2) {//code}
Scanner number = new Scanner(System.in); // Reading from System.in
System.out.println("Enter a two digit number (10-99) ");
int n = 0;
if(number.hasNextInt()) {
n = number.nextInt();
} else {
number.next(); //Clear bad input
System.out.println("Invalid");
}
int m = 0;
if ( n< 10 || n > 99) {
System.out.println("this isnt a valid input and you have killed my program ;(");
}
System.out.println("Enter another two digit number (10-99) ");
if(number.hasNextInt()) {
m = number.nextInt();
} else {
number.next();
System.out.println("Invalid");
}
if (n< 10 || n > 99) {
System.out.println("this isnt a valid input and you have killed my program ;(");
}
int sum = n + m;
System.out.println(sum);

Using arrays to store primes

Here is my program which is supposed to create an array and initialize prime numbers to it. The prime numbers should then be printed but the program just keeps running.
import java.util.*;
public class primes
{
public static void main(String[] args)
{
Scanner scan = new Scanner(System.in);
System.out.println("Enter number of primes ");
int x = scan.nextInt();
int[] prime = new int[x];
int div=2,hold=2;
int c=0;
while (prime[x-1]==0)
{
for(int a=2; div>a;a++)
{
if(div>a && div%a==0)
a=div;
else if(div==(a-1))
hold=div;
}
if(div==2||hold!=prime[c-1])
{
prime[c]=hold;
c++;
}
div++;
}
for(int f =0; f<x;f++)
System.out.print(" "+prime[f]+" ");
}
}
I tried changing my loops but I just don't know whats wrong

Like the others mentioned your logic is not right, try something like:
public static void main(String args[]) {
Scanner scan = new Scanner(System.in);
System.out.println("Enter number of primes ");
int x = scan.nextInt();
List<Integer> primes = getPrimes(x);
Integer[] primeArray = primes.toArray(new Integer[primes.size()]);
for(int i :primes.toArray(primeArray)){ // you could just use for(int i :primes){ if you don't need array
System.out.print(i + " ");
}
}
private static List<Integer> getPrimes(int upperLimit) {
ArrayList primes = new ArrayList();
for (int i = 2; i < upperLimit; i++) {
boolean isPrime = true;
// Is it prime?
for (int j = 2; j < i; j++) {
if (i % j == 0) {
isPrime = false;
break;
}
}
if (isPrime)
primes.add(i);
}
return primes;
}
The above will print out up to the numbers entered so if you type 5 it will print out 2 3 but not 5.
The following is an other example with Java 8, this one will print as many prime numbers based on the input, if you input 5 you will get 2 3 5 7 11
public static void main(String args[]) {
Scanner scan = new Scanner(System.in);
System.out.println("Enter number of primes ");
int x = scan.nextInt();
long[] prime = primes(x).toArray();
Arrays.stream(prime).forEach(value -> System.out.print(value + " " ));
}
private static LongStream primes(long max) {
return LongStream.iterate(2, i -> i + 1)
.filter(PrimeNumber::isPrime)
.limit(max);
}
private static boolean isPrime(long x) {
return LongStream.rangeClosed(2, (long)(Math.sqrt(x)))
.allMatch(n -> x % n != 0);
}

Your code is wrong. First correct it, And i think you want to store prime numbers coming in range of 1 to N where N is user provided number. Use arrayList (growable) to store it.

It will keep on running because you have this: while (prime[x-1]==0). Where x is an input from the user. Say 5 for instance, then prime[5-1] initially is going to contain a 0 always, and you are running your while loop on this condition which is always going to turn true, thus never ending. Also, your prime number generation logic is not right!

I ran your code in debugger mode and I found the problem.
I tested your program with x=5.
At the end of the first while loop iteration you have :
prime[0] = 2
div = 3
hold = 2
c = 1
And here's the problem :
if(div==2||hold!=prime[c-1])
{
prime[c]=hold;
c++;
}
This part won't ever be reached anymore because :
div is never decrement, so it will always be superior to 2.
hold is
equal to prime[c-1], and never change value.
So prime will always stick to be : 2 0 0 0 0, and your while loop will never end.

I found what was wrong and rewrote the code, it works now. The program asks the user for the number primes they want to see and it prints them after storing them in a basic integer array.
import java.util.*;
public class Prime
{
public static void main(String [] args)
{
Scanner scan= new Scanner(System.in);
int i=0, hold=2, d=2;
boolean flag = true;
System.out.println("Enter the number of primes.");
int[] prime= new int[scan.nextInt()];
for(;flag;){
for(int a=2;d>a;a++){
if(d==(a)||d%a==0){
break;
}
if((d-1)==a){
hold = d;
}
}
d++;
if(hold==2 || hold!=prime[i-1]){
prime[i] = hold;
i++;
}
if(i==prime.length)
flag= false;
}
for(int x=0;x<prime.length;x++)
System.out.print(prime[x]+" ");
System.out.println("");
}
}

Why won't my code take the input from the command line?

The point of this program is to take a three digit number from the command line and then reversing it. After that it is supposed to subtract the reverse from the original number and add the original to the reversed.
This is supposed to only take numbers that are three digits and the first digit of the number has to be greater than the last so that it is not negative when the numbers are subtracted.
The code compiles correctly but when I put a number in the command line prints out the line "Enter a three digit number, with the first digit larger than the third" only.
What it is supposed to print out like
$ java Rev 351
Reverse and subtract:
351
153 -
---
198
Reverse and add:
198
891 +
---
1089
This is my code:
public class Rev
{
public static void main(String[] args)
{
int num = 0;
for (int i = 0; i < args.length; i++)
{
System.out.println("Enter a three digit number, with the first digit larger than the third");
num = Integer.parseInt(args[i]);
reverseNum(num);
subtractNum(num);
addNum(num);
}
}
static boolean checkDigits(int number) // checks if numbers are correct
{
int reverse = reverseNum(number);
if(number > reverse)
{
throw new Error("Reverse number needs to be less than the original number!");
}
else
{
return true;
}
}
static int reverseNum(int number) //reverses number
{
int reverse = 0;
int r = 0;
while (number != 0)
{
if(number < 1000 || number > 99)
{
r = number % 10;
reverse = (reverse*10) + r;
number = number/10;
}
}
return reverse;
}
static void subtractNum(int number) // subtracts
{
int reverse = reverseNum(number);
int total = number - reverse;
System.out.println("Reverse and subtract: ");
System.out.println(number);
System.out.println(reverse + " - ");
System.out.println("---");
System.out.println(total);
System.out.println();
number = total;
}
static void addNum(int number) // adds
{
int reverse = reverseNum(number);
int total = number + reverse;
System.out.println("Reverse and add: ");
System.out.println(number);
System.out.println(reverse + " + ");
System.out.println("---");
System.out.println(total);
number = total;
}
}

public static void main(String[] args)
{
int num = 0;
for (int i = 0; i < args.length; i++)
{
System.out.println("Enter a three digit number, with the first digit larger than the third");
num = Integer.parseInt(args[i]);
reverseNum(num);
subtractNum(num);
addNum(num);
}
}
So the args variable is the command line argument. So if you're compiling via command line, you would call something like java Rev.class 321 where 321 is your 3 digit number. If you want to use the Java console to take inputs, use a Scanner.
To take inputs, use something like this:
Scanner sc = new Scanner(System.in);
num = sc.nextInt();

You're never actually getting a number from the input. You need to do this in your main():
public static void main(String[] args)
{
int num = 0;
for (int i = 0; i < args.length; i++)
{
System.out.println("Enter a three digit number, with the first digit larger than the third");
try (Scanner s = new Scanner(System.in)){
num = s.nextInt();
}
reverseNum(num);
subtractNum(num);
addNum(num);
}
}
The Scanner reads the main input stream (from the keyboard). Otherwise, when you pass in the argument on the command line, it hasn't yet asked you for the input, and prints out the request for input.
Your other problem is that you don't call checkDigits() after getting your number, so you should probably do a while loop using it until you get a number you'll accept, like this:
public static void main(String[] args)
{
int num = -1;
while (num < 0 || !checkDigits(num)){
System.out.println("Enter a three digit number, with the first digit larger than the third");
try (Scanner s = new Scanner(System.in)){
num = s.nextInt();
}
}
reverseNum(num);
subtractNum(num);
addNum(num);
}
Also, your other methods are incorrect in that they are acting on an input parameter (which is possible for objects but not primitives, and is bad practice in any case).
Instead write them as functions which take in values and return them, then modify your main again to look like this:
public static void main(String[] args)
{
int num = Integer.parseInt(args[0]);
if (checkDigits(num)){
num = subtractNum(num);
addNum(num);
} else {
System.out.println("Enter only a three digit number, with the first digit larger than the third");
}
}

Binary and linear search program to find an integer. Responds yes if it is there and no if it is not. How to get the binary search working?

I am trying to get the binary search working. It is supposed to ask you to an array size, the integers to be inputted in the array and search the array to find a number you are looking for along with how many probes it took to find it or responds with number not found. I am following the algorithm but it either responds with an infinite loop or not at all because it runs forever. Any suggestions?
package assignment3;
import java.util.Scanner;
public class search{
public static void main(String[] arg){
Scanner range=new Scanner(System.in);
System.out.println("Pick your array size.");
int element=range.nextInt();
int[] array=new int[element];
Scanner array_list=new Scanner(System.in);
if(element<=0){
System.out.println("The array size you chose is not supported. You must chose again");
Scanner tryagain=new Scanner(System.in);
System.out.println("Try again");
element=tryagain.nextInt();
}
System.out.println("Now enter all the numbers in your array");
String list=array_list.nextLine();
String[] newlist=list.split("\\ ");
int lengthofarray=newlist.length;
for(int i=0; i<lengthofarray; i++){
array[i]=Integer.parseInt(newlist[i]);
System.out.println(i+" || "+array[i]);
}
Scanner linearSearch=new Scanner(System.in);
System.out.println("Pick a number to see if it is in the array and how many times it took to find it.");
int linear=linearSearch.nextInt();
Scanner linear2=new Scanner(System.in);
System.out.println("Now we will try the same thing with a binary search. Pick a number");
int binarysearch=linear2.nextInt();
int low=0;
int high=lengthofarray-1;
int middle;
while(low<=high){
middle=(low+high)/2;
if(array[middle]>binarysearch){
high=middle-1;
}
else if(array[middle]<binarysearch){
low=middle+1;
}
}
if(array[low]==binarysearch){
System.out.println("Your number is in the array.");
}
else{
System.out.println("your number is not in the array.");
}
}
}

The problem, I think, is that you miss the case when array[middle] == binarysearch. Look at the logic of your binary search and you'll see that neither low nor high is changed and the loop will never terminate.
Try this instead:
while (low <= high) {
middle = (low + high) / 2;
if (array[middle] > binarysearch) {
high = middle - 1;
} else if (array[middle] == binarysearch) {
low = middle;
break;
} else {
low = middle + 1;
}
}

/*PROGRAM FOR BINARY SEARCH*/
#include<stdio.h>
#include<conio.h>
void main()
{
int arr[100];
int a,n,i,item,loc,temp;
clrscr();
n=1;
loc=0;
printf("\n\Enter total no of data: ");
scanf("%d",&a);
for(i=0;i<a;i++)
{
printf("\n Enter a[%d]:",i);
scanf("%d",&arr[i]);
loc=loc+1;
}
printf("\nEnter ITEM u want to search:");
scanf("%d",&item);
temp=loc+1;
arr[temp]=item;
while(n<=a && arr[n]!=item)
{
n=n+1;
}
if(n==arr[temp])
{
n=0;
printf("\nn=%d",n);
}
else
{
printf("\n ITEM is present AT a[%d]",n);
}
getch();
}