Develop Reference

Making an Armstrong number checker but if condition is not working

I was making an Armstrong number checker not for only 3 digits numbers for which I used Math.pow() method but after using it the if else statement is not working also when the condition is true.
Here is the code:
import java.util.Scanner;
import java.lang.Math;
class Main {
////////////////////////////////////////////
////////////////////////////////////////////
public static void main(String args[])
{
System.out.println("Hello world!");
Scanner sc = new
Scanner(System.in);
int num = sc.nextInt();
int numc = num ;
double rem = 0;
double cu = 0;
int val = 0;
int val2 = 0;
while(num != 0){
rem = num%10;
while(numc != 0){
numc /=10;
int i = 0;
i++;
val2 += i;
}
cu = Math.pow(rem,val2 );
val += cu;
num /= 10;
}
if(val == numc){
System.out.println("Yes its a "+val2+" Armstrong number because its returning " + val+"after Calculations ");
}
else{
System.out.println("No its not a "+val2+" digit Armstrong number because its returning " + val +" after Calculations ");
}
}
}
///////////////////////////////////////////
And this is the Compilation of my code:

if(val == numc){ - This if part is the root cause of your problem . you are dividing numc by 10 for calculations . So at the end it will become 0 . so you will be checking if val == 0 which goes to the else loop.
So I would suggest to assign the input from the user to another variable which you can use for checking the final if - else part.
Like int input = num and at the end if(val==input){ . This would resolve your issue.

The num and numc become zero due to "/= 10" operation. Hence the if condition fails.
Also you need not compute the length of integer every time.
Don't have the reputation to comment hence giving a full fledged solution.
Following is my solution to your problem.
All the best!
import java.util.Scanner;
import java.lang.Math;
class Main {
////////////////////////////////////////////
////////////////////////////////////////////
public static void main(String args[]) {
System.out.println("Hello world!\n");
Scanner sc = new Scanner(System.in);
int num = sc.nextInt();
int numc = num;
double rem = 0;
double cu = 0;
int val = 0;
int val2 = countNumOfDigits(num);
while (num != 0) {
rem = num % 10;
cu = Math.pow(rem, val2);
val += cu;
num /= 10;
}
if (val == numc) {
System.out.println("Yes its a " + val2 + " digit Armstrong number because its returning " + val
+ "after Calculations ");
} else {
System.out.println("No its not a " + val2 + " digit Armstrong number because its returning " + val
+ " after Calculations ");
}
}
private static int countNumOfDigits(int number) {
if (number < 100000) {
if (number < 100) {
if (number < 10) {
return 1;
} else {
return 2;
}
} else {
if (number < 1000) {
return 3;
} else {
if (number < 10000) {
return 4;
} else {
return 5;
}
}
}
} else {
if (number < 10000000) {
if (number < 1000000) {
return 6;
} else {
return 7;
}
} else {
if (number < 100000000) {
return 8;
} else {
if (number < 1000000000) {
return 9;
} else {
return 10;
}
}
}
}
}
}

Comparing Two Strings One Character at a Time in Java

I am trying to compare two different strings, one character at a time. I need to return the correct number of digits until they do not equal each other anymore. However, I can't include the character of '.' in the return statement. How would I go about doing this?
import java.util.Scanner;
import java.math.BigDecimal;
public class PiEstimate {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
String a;
String b;
char y;
char c;
char d;
String userInput;
do {
System.out.print("Enter a number of randomly generated points:");
userInput = in.nextLine();
if (!isValid(userInput)) {
System.out.print("\n" + "You entered an invalid integer. Please enter a valid integer greater than 0: ");
userInput = in.nextLine();
BigDecimal estimate = new BigDecimal((Math.PI / 4) * 4);
estimate.toString();
System.out.println("\n" + "Your estimate is: " + calculation(userInput));
System.out.println("\n" + "Accuracy of digits is :" + comparison(estimate.toString(),userInput));
} else {
BigDecimal estimate = new BigDecimal((Math.PI / 4) * 4);
estimate.toString();
System.out.println("\n" + "Your estimate is: " + calculation(userInput));
System.out.println("\n" + "Accuracy of digits is :" + comparison(estimate.toString(),userInput));
}
System.out.println("\n" + "Would you like to play again? Enter 'Y' for yes or 'N' for no: ");
String optionToPlay = in.nextLine();
c = optionToPlay.charAt(0);
d = Character.toUpperCase(c);
if (d == 'n' || d == 'N') {
BigDecimal estimate2= new BigDecimal( (Math.PI / 4) * 4);
System.out.println("\n" + "The best estimate is: " + estimate2);
}
} while (d == 'Y');
} // end psvm
public static boolean isValid(String a) {
boolean isFlag = true;
char holder;
for (int i = 0; i < a.length(); i++) {
holder = a.charAt(i);
if (!Character.isDigit(a.charAt(i))) {
return false;
} if (i == 0 && holder == '-') {
return false;
}
} // end for
return isFlag;
} // end isValid
public static double calculation(String a) { // String a means 'looking for a string
double calc = Double.parseDouble(a);
int i;
double x;
double y;
double c = 0;
double runningCounter = 0;
double totalCounter;
for (i = 0; i < calc; i++) {
x = Math.random();
y = Math.random();
c = Math.sqrt((x * x) + (y * y));
if (c <= 1) {
runningCounter++;
}
} // end for
totalCounter = ((runningCounter / calc) * 4);
calc = totalCounter;
return calc;
}
public static int comparison (String bear, String userInput) {
int i = 0;
String s = calculation(userInput) + "";
int b;
int counter2 = 0;
for (i=0; i < s.length(); i++) {
if (s.charAt(i) != bear.charAt(i)) {
return i;
}
}
return i;
} // end comparison
} // end class
Code from IDE

How to give input array[] using scanner without space?

In this below program, I'm trying to check whether the number is ISBN or not. I'm giving input with spaces (eg: 0 3 0 6 4 0 6 1 5 2) because array only accepts it like this. I don't know how to give input without space to read. Can anyone help me how to read the number eg: 0306406152 and also it will read 10 numbers only like if(i==10) else it says it's not ISBN number to give output.
public class ISBN {
int digits[];
int dig = 11;
int sum;
int isbn1;
public void CheckISBN() {
for (int digit : digits) {
// System.out.println(digit);
if (dig >= 1) {
dig--;
digit = digit * dig;
// System.out.println(dig);
}
sum = sum + digit;
isbn1 = sum % 11;
}
if (isbn1 == 0) {
System.out.println(isbn1);
System.out.println("it's valid ISBN number");
} else {
System.out.println("sorry it's not valid ISBN");
}
}
public static void main(String[] args) {
ISBN aa = new ISBN();
aa.digits = new int[10];
Scanner scan = new Scanner(System.in);
int i = 0;
while (scan.hasNextInt()) {
aa.digits[i] = scan.nextInt();
i++;
if (i == 10) // aa.CheckISBN();
{
break;
}
for (int j = 0; j < aa.digits.length; j++) {
// System.out.print(aa.digits[j]);
}
//System.out.println();
}
aa.CheckISBN();
}
}
SAMPLE OUTPUT: 0 3 0 6 4 0 6 1 5 2
it's valid ISBN number

When the number is given without spaces,
import java.io.*;
import java.util.*;
public class ISBN {
int digits[];
int dig = 11;
int sum;
int isbn1;
public void CheckISBN() {
if(this.digits.length != 10)
{
System.out.println("sorry it's not valid ISBN");
return;
}
for (int digit : digits) {
// System.out.println(digit);
if (dig >= 1) {
dig--;
digit = digit * dig;
// System.out.println(dig);
}
sum = sum + digit;
isbn1 = sum % 11;
}
if (isbn1 == 0) {
//System.out.println(isbn1);
System.out.println("it's valid ISBN number");
} else {
System.out.println("sorry it's not valid ISBN");
}
}
public static void main(String[] args) {
ISBN aa = new ISBN();
Scanner scan = new Scanner(System.in);
String num = scan.next(); //take input as a string
int[] digits = new int[num.length()];
for(int i = 0; i<digits.length; i++)
digits[i] = num.charAt(i) - '0';
aa.digits = digits;
aa.CheckISBN();
}
}

Or scan it as int to get number format validation for free:
public class ISBN {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
if (scan.hasNextInt()) {
checkISBN(scan.nextInt());
}
}
public static void checkISBN(int isbn) {
int sum = sum(digits(isbn));
int isbn1 = sum % 11;
if (isbn1 == 0) {
System.out.println(isbn1);
System.out.println("it's valid ISBN number");
} else {
System.out.println("sorry it's not valid ISBN");
}
}
private static int sum(int[] digits) {
return IntStream.rangeClosed(1, digits.length)
.map(i -> i * digits[digits.length - i])
.sum();
}
private static int[] digits(int isbn) {
return Integer.toString(isbn)
.chars()
.map(c -> c - '0')
.toArray();
}
}
N.B.: It works for ISBN both with or without leading zeros.

Creating a Palindrome identifier

How can I add a statement that allows me to check if the credit card number inputted by the user is a palindrome? I am checking for the appropriate length already so how can i Input the new palindrome checker into this code:
import java.util.Scanner;
public class DT18 {
public static void main(String[] args) {
String number;
Boolean debug = false;
if (args.length == 0) { // no command line
Scanner keyboard = new Scanner(System.in);
System.out.print("Please enter a Credit Card number to validate.");
number = keyboard.next();
} else { // command line input
number = args[0];
}
if (debug) System.out.println("String Length " + number.length());
if (number.length() < 10) {
System.out.println("Not Valid");
}
int sum = 0;
int oddDigit = 0;
for (int i = number.length() - 1; i >= 0; i--) {
if (debug) System.out.println("i = " + i);
if ((Character.getNumericValue(number.charAt(i)) < 0) || (Character.getNumericValue(number.charAt(i)) > 9)) {
System.out.println("Not Valid");
break;
}
if (i % 2 == 0) { //Even Digit
sum += Character.getNumericValue(number.charAt(i));
} else { //Odd Digit
oddDigit = (2 * Character.getNumericValue(number.charAt(i)));
if (oddDigit > 9) oddDigit = (oddDigit % 10) + 1;
sum += oddDigit;
}
if (debug) System.out.println(sum);
}
if (sum % 10 == 0) {
System.out.println("Valid");
} else {
System.out.println("Not Valid");
}
}
}

From an answer I once gave here:
public boolean isPalindrom(int n) {
return new StringBuilder("" + n).reverse().toString().equals("" + n);
}

This post should give you for loop logic:
http://www.programmingsimplified.com/java/source-code/java-program-check-palindrome
public static void main(String args[])
{
String original, reverse = "";
Scanner in = new Scanner(System.in);
System.out.println("Enter a string to check if it is a palindrome");
original = in.nextLine();
int length = original.length();
for ( int i = length - 1; i >= 0; i-- )
reverse = reverse + original.charAt(i);
if (original.equals(reverse))
System.out.println("Entered string is a palindrome.");
else
System.out.println("Entered string is not a palindrome.");
}

You can write a simple function to check if a string is a palindrome or not.
private static boolean checkPalindrome(String input) {
int i = 0, j = input.length() - 1;
for (; i < j; i++) {
if (i == j) {
return true;
}
if (input.charAt(i) == input.charAt(j)) {
j--;
}
else
return false;
}
return true;
}
This is a crude method; you may want to modify it according to your requirement, but it will get the job done in most of the cases.

I've looked over the other answers and all of them have bad performance and working with String instead of just using the given number. So I'll add the version without conversion to String:
public static boolean isPalindrome(int n) {
int[] digits = new int[length(n)];
for (int i = 0; n != 0; ++i) {
digits[i] = n % 10;
n /= 10;
}
for (int i = 0; i < digits.length / 2; ++i) {
if (digits[i] != digits[digits.length - i - 1]) {
return false;
}
}
return true;
}
public static int length(int n) {
int len = 0;
while (n != 0) {
++len;
n /= 10;
}
return len;
}
Not sure, if that's the best implementation, but I got rid of Strings :-)

Program lists all primes between 0 and n, but also includes 4, 6, and 8

This is my code.
public class PrimeNumbers
{
private int upperLimit;
public PrimeNumbers()
{
}
public boolean isPrime(int c)
{
boolean x = true;
for(int i = 3; i < (int)(Math.sqrt(c)) + 1; i++)
{
if(c % i == 0)
{
x = false;
}
if(c % 2 == 0)
{
x = false;
}
}
return x;
}
public void countPrimes(int upperLimit)
{
this.upperLimit = upperLimit;
int counter = 0;
System.out.println("The prime numbers between 1 and " + this.upperLimit + " are:");
for(int n = 1; n < this.upperLimit; n++)
{
if(isPrime(n))
{
System.out.println(n);
counter++;
}
}
System.out.println("The amount of prime numbers between 1 and " + this.upperLimit + " is: " + counter);
}
}
Here is my Tester Class.
import java.util.Scanner;
public class PrimeNumbersTester
{
public static void main(String[] args)
{
PrimeNumbers a = new PrimeNumbers();
Scanner in = new Scanner(System.in);
System.out.println("Please enter the upper limit.");
int upperLimit = in.nextInt();
a.countPrimes(upperLimit);
}
}
I tested this program using 1000. It seems to list all of the prime numbers in the range, but it also lists 4, 6, and 8, which are not prime numbers. I am unsure what is causing this.

The function should be look like this I thing this will work :
public boolean isPrime(int c)
{
boolean x = true;
int j;
for (j=2; j<c;j++)
{
if(c%j==0)
{
break;
}
}
if(c==j)
{
return true;
}
return false;
}