Develop Reference

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

Counting vowels in a string and wrong output?

I am very new to java and I was wondering if you could help me out. Here is my code:
public static void main(String[] args) {
int vowels = 0;
Scanner input = new Scanner(System.in);
System.out.println ("Enter a string: ");
String string = input.nextLine();
int length = string.length();
for (int i = 0; i <= length; i++) {
String letter = string.substring(i, ++i);
if (letter.equalsIgnoreCase("a")){vowels++;}
if (letter.equalsIgnoreCase("e")){vowels++;}
if (letter.equalsIgnoreCase("i")){vowels++;}
if (letter.equalsIgnoreCase("o")){vowels++;}
if (letter.equalsIgnoreCase("u")){vowels++;}
}
System.out.println ("The number of vowels in " + string + " is: " + vowels);
}
The number is off but I can't figure out why.

This here is wrong
string.substring(i, ++i)
because the variable i is already incremented in the for-loop
so you are basically skipping chars in the string
implement the right logic, use the right data type
int length = string.length();
for (int i = 0; i < length; i++) {
char letter = string.charAt(i);
System.out.println(letter);
if (letter == 'a') {
vowels++;
} else if (letter == 'e') {
vowels++;
} else if (letter == 'i') {
vowels++;
} else if (letter == 'o') {
vowels++;
} else if (letter == 'u') {
vowels++;
}
}

Here is another solution you could try:
The split method will split the string into a String array. Then in your for loop it will check every item in your array.
public static void main(String[] args) {
int vowels = 0;
Scanner input = new Scanner(System.in);
System.out.println ("Enter a string: ");
String string = input.nextLine();
int length = string.length();
String[] stringArray = string.split("");
for (int i = 0; i < length; i++) { //I took out the = sign in your for loop arguments.
if (stringArray[i].equalsIgnoreCase("a")){vowels++;}
if (stringArray[i].equalsIgnoreCase("e")){vowels++;}
if (stringArray[i].equalsIgnoreCase("i")){vowels++;}
if (stringArray[i].equalsIgnoreCase("o")){vowels++;}
if (stringArray[i].equalsIgnoreCase("u")){vowels++;}
}
System.out.println ("The number of vowels in " + string + " is: " + vowels);
}

Hangman never prints 'You won'

Just started a computer science degree and have been tasked with making a Hangman game, it seems to work find other than it doesn't print "You won" and I cannot see/figure out why it doesn't. Any help from you guys would be great.
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
Random rand = new Random();
char[] alpha = new char[26];
Arrays.fill(alpha, ' ');
String a1 = "intro to programming";
String a2 = "computer";
String a3 = "mouse and keyboard";
String a4 = "skyrim";
String a5 = "hello world";
int selector = rand.nextInt(5) + 1;
char[] words = null;
char[] show = null;
if (selector == 1) {
words = a1.toCharArray();
show = a1.toCharArray();
Arrays.fill(show, '-');
} else if (selector == 2) {
words = a2.toCharArray();
show = a2.toCharArray();
Arrays.fill(show, '-');
} else if (selector == 3) {
words = a3.toCharArray();
show = a3.toCharArray();
Arrays.fill(show, '-');
} else if (selector == 4) {
words = a4.toCharArray();
show = a4.toCharArray();
Arrays.fill(show, '-');
} else if (selector == 5) {
words = a5.toCharArray();
show = a5.toCharArray();
Arrays.fill(show, '-');
}
int length = words.length;
System.out.println("Please enter the amount of tries you would like:");
int amount = scan.nextInt();
String guessed;
char guessedchar;
for (int i = 0; i < length; i++) {
if (words[i] == ' ') {
show[i] = ' ';
}
}
int x = 0;
while (amount >= 0) {
System.out.print("String to guess: ");
for (char n : show) {
System.out.print(n);
System.out.print(" ");
}
System.out.println(" ");
System.out.println("Number of tries left: " + amount);
System.out.print("Number of times you have tried: ");
for (char a : alpha) {
System.out.print(a);
System.out.print(" ");
}
System.out.println(" ");
System.out.println("Enter a guess");
guessed = scan.next();
guessedchar = guessed.charAt(0);
alpha[x] = guessedchar;
for (int i = 0; i < length; i++) {
if (guessedchar == words[i]) {
show[i] = guessedchar;
}
}
x = x + 1;
amount = amount - 1;
if (amount == 0) {
System.out.println("You lose");
return;
} else if (show == words) {
System.out.println("You won");
}
}
}

Convert the words and show arrays to Strings and check if they are equal with .equals(), this should then display the correct message

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 :-)

Java phrase guessing game

Wondering how to exit if total phrase is guessed and why my vowels, spaces and consonants are not counting? Most of progam runs great just cant figure out how to exit without saying "n" to question. I am returning values for counters, don't understand?
import java.util.Scanner;
public class Prog09
{
public static void main(String[] args)
{
Scanner stdIn = new Scanner(System.in);
// Initializes all string variables
String sPhrase;
String answer;
// Initializes all int variables
int vowels = 0;
int consonants = 0;
int spaces = 0;
// Initializes all char variables
char cGuess = 0;
char vGuess = 0;
boolean valid = false;
// Asks user to enter if they want to play
System.out.print("Do you want to play a game? [y/n] ");
answer = stdIn.nextLine();
// Asks user to enter the phrase
System.out.print("Please enter the phrase to guess at : ");
sPhrase = stdIn.nextLine();
// Checks if user wants to play
while (answer.equalsIgnoreCase("y"))
{
char[] phrase = new char[sPhrase.length()];
char[] tmpArr = new char[sPhrase.length()];
for(int i = 0; i < sPhrase.length();i++)
{
tmpArr[i] = sPhrase.charAt(i);
phrase[i] = sPhrase.charAt(i);
}
// Runs methods and main body of program
initTemplateArray(sPhrase, tmpArr, spaces);
printHeader();
printTemplateArray(tmpArr);
System.out.println("");
System.out.println("");
while (answer.equalsIgnoreCase("y"))
{
//getConsonant(stdIn, cGuess);
cGuess = getConsonant(stdIn, cGuess);
vGuess = getVowel(stdIn, vGuess);
isVowel(vGuess, valid);
updateTemplateArray(tmpArr, sPhrase, cGuess, vGuess, consonants, vowels);
printHeader();
printTemplateArray(tmpArr);
System.out.println("");
System.out.println("");
stdIn.nextLine();
System.out.print("Do you want to try again? [y/n]: ");
answer = stdIn.next();
vGuess = 0;
cGuess = 0;
}
}
// Prints results
System.out.println("The common phrase contained: Spaces: " + spaces + " Consonants: " + consonants + " Vowels: " + vowels);
stdIn.close();
}
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Methods for program
public static int initTemplateArray(String sPhrase, char [] tmpArr, int spaces)
{
for (int i = 0; i < sPhrase.length(); i++)
{
if (sPhrase.charAt(i) == ' ')
{
spaces++;
tmpArr[i] = ' ';
}
if (!(sPhrase.charAt(i) == ' '))
{
tmpArr[i] = '?';
}
}
return spaces;
}
public static void printTemplateArray(char [] tmpArr)
{
for (int i = 0; i < tmpArr.length; i++)
{
System.out.print(tmpArr[i]);
}
System.out.println();
}
public static boolean isVowel(char c, boolean valid)
{
if(c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u')
{
return valid = true;
}
else
{
return valid = false;
}
}
public static char getConsonant(Scanner stdIn, char cGuess)
{
while(cGuess == 'a' || cGuess == 'e' || cGuess == 'i' || cGuess == 'o' || cGuess == 'u'|| cGuess == 0)
{
System.out.print("Enter a lowercase consonant guess : ");
String myGuess = stdIn.next();
cGuess = myGuess.charAt(0);
}
return cGuess;
}
public static char getVowel(Scanner stdIn, char vGuess)
{
while(!(vGuess == 'a' || vGuess == 'e' || vGuess == 'i' || vGuess == 'o' || vGuess == 'u'))
{
System.out.print("Enter a lowercase vowel guess : ");
String newGuess = stdIn.next();
vGuess = newGuess.charAt(0);
}
return vGuess;
}
public static int updateTemplateArray(char [] tmpArr, String sPhrase, char cGuess, char vGuess, int consonants, int vowels)
{
vowels = 0;
consonants = 0;
for (int i = 0; i < tmpArr.length; i++)
{
if (cGuess == sPhrase.charAt(i))
{
tmpArr[i] = sPhrase.charAt(i);
consonants++;
}
if (vGuess == sPhrase.charAt(i))
{
tmpArr[i] = sPhrase.charAt(i);
vowels++;
}
}
return consonants & vowels;
}
public static void printHeader()
{
System.out.println("");
System.out.println(" Common Phrase");
System.out.println("---------------");
}
}

Java passes Ints by value instead of by reference, this means that updateTemplateArray doesn't modify the values of main's vowels, consonants or spaces. To fix this you could:
Make these variables global by definining them outside the scope of the main method. You would have to change the name of the parameters in the updateTemplateArray method to prevent shadowing.
Break updateTemplateArray into separate functions to count each of the vowels, consonants or spaces, and have them return the count of each. You would then call something like: vowels = countVowels(sPhrase); to populate the variables.
With the current setup, it will exit whenever answer stops being equal to 'y' Changing the value of answer at any time will exit the loop.