Develop Reference

Some weird interactions are happening in my code, but I can't find a solution

My code for calculating average is correct but my program wont stop executing they way I want it to. I have to use scanner's functions in order to manipulate the string.
So I wanted to get better at Java and my tutor gave me a problem to solve. The program must accept student id, name of the subject and its marks, all in one string, and then calculate the average marks for this id. The format of the sting is "123456 math 5.5 physics 6.5 end" where the 6 digit number is the id and "end" is what makes the program stop waiting for numbers and calculate them.
ID is a 6 digit number from 0 to 9 which if it is 000000 the program must terminate.
"End" is stopping the entry but not the loop, but "000000" ends the loop.
In my code everything works fine but in order for the variables I use to reset I must type two times the word "end" and if I want to stop the loop I must type "000000" twice which is clearly not what I want. Can you point out my mistakes?
My teacher suggested to use Scanner's functions in order to get what I want. Is this problem something I cannot solve because of they way these functions work?
package averagemarks;
import java.util.*;
class AverageMarks {
public static void main(String args[]) {
String s = "123456 pr1 6.2 pr2 7.3"; //string input format
Scanner sc = new Scanner(System.in);
sc.useDelimiter("\\s+"); //space to split string tokens
sc.useLocale(Locale.US); //with that it can recognise float numbers
int count = 0;
double sum = 0.0;
String AM; //6 numbers from 0-9 consists the student id
System.out.println("Give string: ");
while(sc.hasNext()) {
String str = sc.next();
if (sc.hasNext("[0-9]{6}")) { //this is where i check for the id which if it is 000000 it must terminate the loop
AM=str;
System.out.println("AM: " + AM);
if (AM.equals("000000")) break;
} else if(sc.hasNext()== false) { //string must end with an end if user does not end it with it i must inform him
System.out.println("Data format error.");
//return;
} else if(sc.hasNextFloat()){ //this is where i gather data for the result
sum += sc.nextFloat();
count++;
} else if(sc.hasNext("end")){ //end means that you gonna calculate all the numbers till that point then reset for another student
System.out.println("Average is " + sum / count);
count = 0;
sum = 0.0;
}
}
}
}

"In my code everything works fine"
Well, it does not!
With the line String str = sc.next(); you read away required data.
You should put it in the end to read the course name away.
while(sc.hasNext()) {
// check student id
if (sc.hasNext("[0-9]{6}")) {
AM=sc.next(); // read student number
System.out.println("AM: " + AM);
if (AM.equals("000000")) break;
}
// check if line ends prematurely --> error
else if(sc.hasNext()== false) {
System.out.println("Data format error.");
//return;
}
// check for a float
else if(sc.hasNextFloat()){
sum += sc.nextFloat(); // read the float
count++;
}
// check for "end"
else if(sc.hasNext("end")){
String endStr = sc.next(); // read "end"
System.out.println("Average is " + sum / count);
count = 0;
sum = 0.0;
}
// all other not yet considered strings (e.g. a course)
else {
String course = sc.next(); // read course
}
}

Try this:
String AM = null; //6 numbers from 0-9 consists the student id
System.out.println("Give string: ");
String str = null;
while(sc.hasNext()) {
if (sc.hasNext("[0-9]{6}"))
{
str = sc.next("[0-9]{6}");
AM = str;
System.out.println("AM: " + AM);
if (AM.equals("000000")) break;
}
else if(sc.hasNext()== false) {
System.out.println("Data format error.");
//return;
}
while(sc.hasNextDouble()){
sum += sc.nextDouble();
count++;
}
if(sc.next().equals("end")){
System.out.println("Average is " + sum / count);
count = 0;
sum = 0.0;
}
}
I did not check if your sc.hasNext()==false works, but everything else seems to working properly. Only type end once to go to next option, "000000" to end entire program. I changed the next float to next double because you had sum declared as a double and put it into a loop so it finds all the next doubles. I moved all the next operations into the conditions as well. Remember that .next() moves to the next one. Your old code with sc.hasNext("end") did not move the cursor at all. Let me know if something is off or if you have a question!

Java - 2-Do-While Loops in a For Loop

I'm quite new to programming so excuse my basic and limited understanding. Essentially, I am creating a Memory Game for a school project. I want to do 2 do-while loops in a for loop that works like this: the user will be prompted to enter a 4 random letters which will be done in the first do-while loop and the second do-while loop will ask the user to re-input the phrase that they had initially entered.
So my first question is, why does only the first do-while execute? I'm assuming that the for loop executes the first-do-while and than repeats based on my parameters therefore the second one will never execute but, I'd appreciate any help understanding why, and reformatting my program accordingly perhaps.
My second question is that, I want to have a sort of score counter that nets the user 10 points for every correctly guessed letter in the correct sequence and deduct 10 for every incorrect character in the wrong sequence. How would I go about doing so, and what may I have to utilize to make this possible?
Lastly, I would appreciate if anyone could point towards a way of concealing the letters that the user inputs.
Any other suggestions to make my program more efficient would be greatly appreciated!
import java.util.Scanner;
import java.lang.String;
public class MemoryGame {
public static void main(String[]args){
Scanner input = new Scanner(System.in);
int choice;
System.out.println("This is a M E M O R Y G A M E");
System.out.println("Press '1' for instructions");
System.out.println("Press '2' to play");
choice = input.nextInt(); //Checks user selection and redirects
if (choice == 1) {
Instructions();
} else {
playGame();
}
input.close();
}
public static void Instructions() { //Instructions method
int choice;
Scanner input = new Scanner(System.in);
System.out.println("This is a memory game. Below are a few instructions on how to play as well as few hints, and tricks");
System.out.println("> Players wlll be given a input box to input a given number of letters or numbers depending on the stage level.");
System.out.println("> To progress and gain points, users must sucessfully recall the set phrase that they have inputted.");
System.out.println("> Based on the number of correct letters, users will gain points and progress through a set of levels that increase in difficulty.");
System.out.println("> Upon making 3 incorrect character selections users will be displayed a 'Game Over' screen from which they may:");
System.out.println("1. Head to the main menu");
System.out.println("2. View the instructions");
System.out.println("3. Play again");
System.out.println("If users successfully oomplete 5 stages with no errors, they will be prompted a challenge level in which more characters will be required");
System.out.println(" ");
System.out.println("1. Press '1' to return to play");
choice = input.nextInt();
if (choice == 1) {
playGame();
}
input.close(); //Closes input.
}
public static void playGame() {
int userNumbers1;
int userNumbers2;
String userLetters1;
String userLetters2;
int scorePlayer;
int livesPlayer = 3;
int stagePlayer = 4;
int stageGeneral = 1;
Scanner input = new Scanner(System.in);
System.out.println("This is the M E M O R Y G A M E");
System.out.println("Stage 1 initializing . . .");
System.out.println("Please enter " + stagePlayer + " letters of your choice.");
for (int i = 0; i <= 10; i++) {
do {
userLetters1 = input.nextLine();
userLetters1 = userLetters1.toLowerCase(); userLetters1.trim();
if (userLetters1.length()==stagePlayer) {
System.out.println (". . .!");
stagePlayer = stagePlayer + 2;
stageGeneral = stageGeneral + 1;
} else {
System.out.println("Please enter " + stagePlayer + " letters");
}
}
while ( userLetters1.length() != stagePlayer);
do {
userLetters2 = input.nextLine();
userLetters2 = userLetters2.toLowerCase(); userLetters2.trim();
if (userLetters2.length()==userLetters1.length() && userLetters2.equals (userLetters1)) {
System.out.println (". . .");
System.out.println ("Great job!");
System.out.println("Stage " + stageGeneral + " initializing . . .");
System.out.println("Please enter " + stagePlayer + " letters of your choice.");
} else {
System.out.println ("Please enter " + userLetters1.length() + "letters that were previously entered.");
}
}
while ( userLetters1.length() != userLetters2.length());
}
}
}

Don't assume. Debug instead. Look what happens line by line and determine the reason the first do lop never exits. It if exited I see no reason why the second one didn't execute.
For second question I'd enciurage to read String class documentation. All you need is to iterate through characters and react accordingly to results of copmarisions.
In console, to hide previous user input you could clear the screen like:
Runtime.getRuntime().exex("cls);

Correct user input not matching array values

I've written a portion of code to take a user input, match it to a string value and then use a related double value to make calculations:
double [] currency = new double[] {0.05,0.10,0.20,0.50,1.00,2.00,5.00,10.00,20.00,50.00,100.00};
String [] currencytext = {"$0.05","$0.10","$0.20","$0.50","$1.00","$2.00","$5.00","$10.00","$20.00","$50.00","$100.00"};
Scanner keyboard = new Scanner(System.in);
for (int i = 0; i < currencytext.length; i++) {
boolean valid = false;
while(!valid){
System.out.format("$%.2f remains to be paid. Enter coin or note: ",sum);
String payment = keyboard.next();
if(payment.equals(currencytext[i])){
sum = sum - currency[i];
if(sum == 0) {
System.out.print("You gave " + payment);
System.out.print("Perfect! No change given.");
System.out.print("");
System.out.print("Thank you" + name + ".");
System.out.print("See you next time.");
}
}
if(!(payment.equals(currencytext[i]))) {
System.out.print("Invalid coin or note. Try again. \n");
}
if(payment.equals(currencytext[i]) && currency[i] > sum){
System.out.print("You gave " + payment);
System.out.print("Your change:");
}
}
}
The problem is that when it gets to user input, it doesn't match any string values except for $0.05. It seems to me like its not iterating through the array properly but I can't figure out why. Is anyone able to see a problem here?

This is a possible solution for your problem
Scanner keyboard = new Scanner(System.in);
double [] currency = new double[] {0.05,0.10,0.20,0.50,1.00,2.00,5.00,10.00,20.00,50.00,100.00};
String [] currencytext = {"$0.05","$0.10","$0.20","$0.50","$1.00","$2.00","$5.00","$10.00","$20.00","$50.00","$100.00"};
String payment = keyboard.next();
double sum = 100; // <- Working example - Read sum from keyboard entry
while (sum > 0) {
boolean paymentFound = false;
for (int i = 0; i < currencytext.length; i++) {
if (payment.equals(currencytext[i])) {
sum = sum - currency[i];
paymentFound = true;
if (sum == 0) {
System.out.println("You gave " + payment);
System.out.println("Perfect! No change given.");
// System.out.print("Thank you" + name + ".");
System.out.println("See you next time.");
break;
} else if (sum < 0) {
System.out.println("You gave " + payment);
System.out.println("Your change:" + (-1 * sum));
break;
}
}
}
if (!paymentFound) {
System.out.println("Invalid coin or note. Try again. \n");
}
if (sum > 0) {
System.out.format("$%.2f remains to be paid. Enter coin or note: ", sum);
payment = keyboard.next();
}
}
while-loop will continue until the payment is fullfilled.
for-loop traverse the arrays until a suitable payment is found
If suitable payment is found we substract it from sum. We use break to exit the for-loop in both cases. There is no need to keep searching.
If no suitable payment is found [!paymentFound], we keep on asking.
if (!paymentFound) {
System.out.println("Invalid coin or note. Try again. \n");
}
if (sum > 0) {
System.out.format("$%.2f remains to be paid. Enter coin or note: ", sum);
payment = keyboard.next();
}
The program will end when (sum < 0), in which case the while-loop exits.
I have use println instead of print to improve message legibility.

Too many flaws to point out.
However,
When the currencytext[i] does not match payment, it executes this code:
System.out.print("Invalid coin or note. Try again. \n");
System.out.format("$%.2f remains to be paid. Enter coin or note: ",sum);
payment = keyboard.next();
So, it executes this for all the times that your input does not match currencytext[i].
And, in this block, you have
payment = keyboard.next();
So, it asks for new input, in this block itself. Hence, you get the said output for all inputs except $0.05.
As far as $0.05 is concerned, your first if block executes successfully, and prints no output. So, it moves to the next iteration of the while loop, where again, payment remains the same ($0.05), but currencytext[i] becomes $0.10. SO they do not match, and you get the said output.
How to correct this:
With this code, you need to do a lot of corrections.
I suggest you again start from scratch.

If it doesn't fit, it sets valid to true, so the code just has the chance to check against the first item at currencytext[0], which is $0.05. Then !payment.equals(currencytext[i]) is also true, and your code prints the lines there. Your else ifs are also not properly nested.

I don't know how you are reading input. One improvement you can do is write reading input code in for loop.
Scanner scanner = new Scanner(System.in);
for (... ) {
....
String payment = scanner.nextLine();
....
}

Problems with a word guessing game

I'm trying to get Java to recognize the output of a while loop as a variable and to use that output in further operations.
I wanted to try and upgrade it by letting one player set the word and the other one guess it. The problem came from making the number of dashes equal to the number of letters in the word that the player entered, so I separated the code out, which worked.
But when I put it all back in main, it would not recognize how many dashes are there after the loop finishes; it only recognizes the initial one which is only 1 dash, and so it poses a problem.
EDIT: Thank you so much guys, its my first time on stack overflow, tnx again.
Works like a charm :D
package iB;
import java.util.Scanner;
import java.lang.String;
public class WordGuess {
/**
* #param args
*/
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
String secretWord ;
String guess, dash = "-", upWord;
int numGuesses = 0;
int numWord;
final String SENTINEL = "!";
System.out.println("Player 2, please look away. Player 1, please enter the secter word: \n");
secretWord = input.next().toUpperCase().trim();
numWord = secretWord.length();
//System.out.println("\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n");
for(int dashNum = 1; dashNum < numWord; dashNum++) {
dash += "-" ;
}
System.out.println("WordGuess game!\n");
do {
System.out.println("Enter a letter (" + SENTINEL + "to guess entire word): ");
guess = input.next().toUpperCase().trim();
numGuesses ++;
if (secretWord.contains(guess) && guess.length() == 1) {
upWord = dash.substring(0, secretWord.indexOf(guess));
upWord += guess;
upWord += dash.substring(secretWord.indexOf(guess) + 1, dash.length());
dash = upWord.toUpperCase();
System.out.println(dash);
if (dash.equals(secretWord)) {
System.out.println("You won!\n" + "The secret word is " + secretWord);
System.out.println("You made " + numGuesses + " guesses."); }
} else if (guess.length() >= 2) {
System.out.println("Please only enter one letter at a time! \n"); }
if (guess.contains(SENTINEL)) {
System.out.println("What is your guess? ");
guess = input.next().toUpperCase().trim();
if (guess.equals(secretWord)) {
System.out.println("You won!\n" + "The secret word is " + secretWord);
System.out.println("You made " + numGuesses + " guesses.");
break;
} else {
System.out.println("You Lose!");
System.out.println("The secret word was " + secretWord);
System.out.println("You made " + numGuesses + " guesses.");
break;
}
}
} while(!guess.contains(SENTINEL));
input.close();
}
}

The problem
The following piece of code appears to be trying to show where in a word the correctly chosen letter can be found
if (SecretWord.indexOf(guess) >= 0) {
UpWord = dash.substring(0, SecretWord.indexOf(guess));
UpWord += guess;
UpWord += dash.substring(SecretWord.indexOf(guess) + 1, dash.length());
System.out.println(UpWord);
} else {
So if the word was this and you guessed i then the output should be
--i-
dash.substring does not repeat dash, it takes a sub part of dash, as dash is 1 letter long, anything other than substring(0,1) will lead to an exception.
Basic solution
I believe you want to repeat dash until you get to the guessed letter, and then after it till the end of the word. Something along the lines of:
if (SecretWord.indexOf(guess) >= 0) {
int guessedIndex=SecretWord.indexOf(guess);
String outString="";
for(int i=0;i<guessedIndex;i++){
outString+=dash; //repeat dash until we get to the correctly guessed letter
}
outString+=guess; //put the letter in
for(int i=guessedIndex;i<SecretWord.length();i++){
outString+=dash; //repeat dash until we get to end of the word
}
System.out.println(outString);
} else {
Better Solution
This however leaves the problem that only the first instance of the letter is shown. This can be solved using annother stack overflow answer in which we see that we can get all the occurances of a character using a function
public static ArrayList<Integer> getAllIndexes(String testChar, String string){
int index=string.indexOf(testChar);
ArrayList<Integer> indexes=new ArrayList<Integer>();
while(index>0){
indexes.add(index);
index=string.indexOf(testChar,index+1);
}
return indexes;
}
Then using that function to find all the indexes at which the letter occurs we can deal with repeated letters
if (SecretWord.indexOf(guess) >= 0) {
int guessedIndex=SecretWord.indexOf(guess);
ArrayList<Integer> indexes=getAllIndexes(guess,SecretWord);
String outString="";
for(int i=0;i<SecretWord.length();i++){
if (indexes.contains(i)){
outString+=guess; //if its one of the guessed letters, put that in
}else{
outString+=dash; //otherwise add a dash
}
}
System.out.println(outString);
} else {
Now a word of hello and a guess of l correctly outputs --LL-
Notes
It is usual to follow the naming convention that variable names are
in lower camel case, meaning they start with a lower case letter, as
such SecretWord should be secretWord. As it is currently written
it looks like SecretWord is a class, which are usually writen in
upper camel case.
It would be nice, if once you've guessed a letter it stops putting a dash in and starts putting the letter in every time after that, this could be achieved by using an array of booleans to check if the letter has been guessed but that is beyond the scope of this question
All of these solutions have appended strings, which can be slow for huge numbers, in your case this is the right thing to do, but is joining lots of strings together in a loop consider using a StringBuilder to remove the overhead of creating loads of intermediate strings

Solution
If the secret word is pony, the String dash should be equal to ----. The problem is that you never actually change dash from being equal to -. Therefore, when you do things like dash.substring(SecretWord.indexOf(guess) + 1, dash.length()), you get errors because dash only contains one character. Here's how I'd make dash the same length as the secret word:
for(int i = 0; i < NumWord; i++) {
dash += "-";
}
With this one change inserted directly before your do-while loop, your program works like a charm. Below are some other things to consider in order to further improve your program.
Improving readability
Java convention dictates that the first word of method and variable names is lowercase. So NumWord should be numWord, SecretWord should be secretWord, etc.
SecretWord.indexOf(guess) >= 0 should be changed to
SecretWord.contains(guess)
Gameplay suggestions
As in hang man, you should probably show all the spots where the guessed letter occurs. For example, if the secret word is happy, a guess of p should produce the output of --PP- instead of --P--.
As a rule, never accept bad input even if it doesn't cause errors. The program shouldn't allow any of the scenarios below:
A user enters a String containing non-alphabetic characters or multiple words as the secret word
When making guesses, non-alphabetic characters are input (excluding !)
When guessing letters, multiple characters are input.

I have made a couple of modifications to your code, it seems to work fine now.
First though, I added an extra method, just to make it a little easier:
public static String printOutWord(String[] UpWord){
String out = "";
for(int i = 0; i < UpWord.length; i++){
out += UpWord[i];
}
return out;
}
Here are the first few changes to you code:
String[] UpWord = new String[NumWord];
for(int i = 0; i < NumWord; i++){
UpWord[i] = "-";
}
printOutWord(UpWord);
System.out.println("\nWordGuess game!");
So, you no longer need the variable dash, and the variable UpWord has been changed to an array of Strings.
And this is the rest of it:
do {
System.out.println("Enter a letter (! to guess entire word): ");
guess = input.next().toUpperCase().trim();
Numguesses++;
if(guess.length() > 1){
System.out.println("Please only enter one letter at a time");
}else if (SecretWord.indexOf(guess) >= 0) {
int index = SecretWord.indexOf(guess);
UpWord[index] = guess;
while(SecretWord.indexOf(guess, index+1) >= index){
index = SecretWord.indexOf(guess, index+1);
System.out.println(index);
UpWord[index] = guess;
}
System.out.println(printOutWord(UpWord));
if(printOutWord(UpWord).equals(SecretWord)){
System.out.println("You won!\n" + "The secret word is " + SecretWord);
return;
}
} else {
if (guess.contains("!")) {
System.out.println("What is your guess? ");
guess = input.next().toUpperCase();
if (guess.equals(SecretWord)) {
System.out.println("You won!\n" + "The secret word is " + SecretWord);
System.out.println("You made " + Numguesses + " guesses");
} else if (!guess.equals(SecretWord)) {
System.out.println("You Lose!");
System.out.println("You made " + Numguesses + " guesses");
}
}
}
} while (!SecretWord.equals(guess));
input.close();
}
Most of the changes are within the first if statement.
I hope this helped, if any clarification is needed about anything, just ask, I'd be happy to help :)

Java input keeps being empty?

This is a simple question selection, and then answer program:
import java.util.Scanner;
public class Mains {
static Scanner console = new Scanner(System.in);
static Tof tof = new Tof();
static int Ievel = 0;
static int Input = 0;
static boolean GAME = true;
static boolean AT_START = true;
static boolean IN_QUESTION = false;
public static void main (String[] args) {
while (GAME) {
String InputS = "";
if (AT_START) {
System.out.println("Welcome to the game! Please select a number from 1 to 10.");
AT_START = false;
}
if (!IN_QUESTION)
Input = console.nextInt();
if (Input == -1) {
GAME = false;
console.close();
} else {
String question = tof.getQuestion(Input);
String answer = tof.getAnswer(Input);
System.out.println(question);
IN_QUESTION = true;
while (IN_QUESTION) {
InputS = console.nextLine();
if (InputS != console.nextLine()) {
if (InputS.equals(answer)) {
System.out.println("Correct!");
} else {
System.out.println("Incorrect. " + InputS + " " + answer);
}
}
}
}
}
}
}
Problem:
When entering the IN_QUESTION loop, and writing a answer, it will always be incorrect.
That's because the InputS variable is ALWAYS empty, no matter what, while it has console.nextLine() set on it.
Why is it empty? How do I fix this?
In-case you need the other class Tof: http://pastebin.com/Fn5HEpL2

nextInt doesn't get the line terminator after the integer and you're reading from the console twice (the second time being in the if-statement).
So if you enter:
123
apple
The following happens:
Input gets assigned a value of 123
InputS gets assigned an empty string
InputS gets compared against apple and it is not equal (from InputS != console.nextLine() - I'm not sure why it's there)
You can fix it by:
Putting a console.nextLine(); after console.nextInt();
OR
Use Input = Integer.parseInt(console.nextLine()) instead of nextInt
Removing this - if (InputS != console.nextLine())

You're reading from the console twice. This should work:
while (IN_QUESTION) {
InputS = console.nextLine();
if (InputS.equals(answer)) {
System.out.println("Correct!");
} else {
System.out.println("Incorrect. " + InputS + " " + answer);
}
}

The problem is that the new line character was not read by the nextInt() method so it remain in the scanner buffer and when the next time you called nextLine() that character was printed first.
This is how to fix the issue:
//empty the newline character from the scanner
console.nextLine();
while (IN_QUESTION) {
InputS= console.nextLine();
if (InputS.equals(answer)) {
System.out.println("Correct!");
} else {
System.out.println("Incorrect. " + InputS + " " + answer);
}
}

You call console.nextLine twice. This means that you read a line that you'll check, and another you won't. This is probably not what you are after. Also note that your initial call of nextInt will not consume the newline you pressed after entering the number. You need a nextLine right after that, but before the main loop.
Some general remarks:
uppercase names are only for constants, so your variables should be lowercase;
you should really be using local variables instead of static ones. Right now this isn't hurting you, but it soon could.