Develop Reference

Stuck While Loop (Java)

all!
I'm a university freshman computer science major taking a programming course. While doing a homework question, I got stuck on a certain part of my code. Please be kind, as this is my first semester and we've only been doing Java for 3 weeks.
For context, my assignment is:
"Create a program that will ask the user to enter their name and to enter the number of steps they walked in a day. Then ask them if they want to continue. If the answer is "yes" ask them to enter another number of steps walked. Ask them again if they want to continue. If they type anything besides "yes" you should end the program by telling them "goodbye, [NAME]" and the sum of the number of steps that they have entered."
For the life of me, I can not get the while loop to end. It's ignoring the condition that I (probably in an incorrect way) set.
Can you please help me and tell me what I'm doing wrong?
import java.util.Scanner;
public class StepCounter
{
/**
* #param args the command line arguments
*/
public static void main(String[] args)
{
final String SENTINEL = "No";
String userName = "";
String moreNum = "";
int numStep = 0;
int totalStep = 0;
boolean done = false;
Scanner in = new Scanner(System.in);
Scanner in2 = new Scanner(System.in);
// Prompt for the user's name
System.out.print("Please enter your name: ");
userName = in.nextLine();
while(!done)
{
// Prompt for the number of steps taken
System.out.print("Please enter the number of steps you have taken: ");
// Read the value for the number of steps
numStep = in.nextInt();
// Prompt the user if they want to continue
System.out.print("Would you like to continue? Type Yes/No: ");
// Read if they want to continue
moreNum = in2.nextLine();
// Check for the Sentinel
if(moreNum != SENTINEL)
{
// add the running total of steps to the new value of steps
totalStep += numStep;
}
else
{
done = true;
// display results
System.out.println("Goodbye, " + userName + ". The total number of steps you entered is + " + totalStep + ".");
}
}
}
}

To compare the contents of String objects you should use compareTo function.
moreNum.compareTo(SENTINEL) return 0 if they are equal.
== operator is used to check whether they are referring to same object or not.
one more issue with addition of steps, addition should be done in case of "No" entered also

Use
if(!moreNum.equals(SENTINEL))
Instead of
if(moreNum != SENTINEL)
Also, make sure to add: totalStep += numStep; into your else statement so your program will actually add the steps together.

I try to make a guess game and let user decide under what max number to guess

In oder to check the value entered by the user AND to see what random number has been calculated, I want to let those numbers projected in the console (eclipse). But what sketches my astonishment?? the last two system.out.println's (right above invoermax.close())) do NOT appear in the console screen after I entered the number???? It's like java doesn't even read or notice these code lines, How come???
Here my code:
package Package1;
import java.util.Scanner;
import java.util.concurrent.ThreadLocalRandom;
public class test6KOPIE1 {
public static void main(String[] args)
{
Scanner Invoermax = new Scanner(System.in);
System.out.println("Under which number you want to guess");
int Invoer = Invoermax.nextInt();
int Hoogte = ThreadLocalRandom.current().nextInt(1,Invoermax.nextInt());
System.out.println("So a guess under max: " + Invoer);
System.out.println("The random number has become " + Hoogte);
Invoermax.close();
}
}

every time you call Scanner.nextInt() it will wait for input from you.
The problem is that you are calling it twice, replace:
int Hoogte = ThreadLocalRandom.current().nextInt(1,Invoermax.nextInt());
With the variable you already got:
int Hoogte = ThreadLocalRandom.current().nextInt(1,Invoer);
And BTW, usually in java you start field/variable name with lower case letter, so should be hoogte, inoverMax, inover etc.

You can do something like this.
// code
Scanner Invoermax = new Scanner(System.in);
System.out.println("Under which number you want to guess");
int Invoer = Invoermax.nextInt();
Invoermax.nextLine(); // reading empty space left
int Hoogte = ThreadLocalRandom.current().nextInt(1,Invoermax.nextInt());
// code

You have two scanner.nextInt() calls, so there are two input readings, two input waitings.
int Invoer = Invoermax.nextInt(); // the first input reading
int Hoogte = ThreadLocalRandom.current().nextInt(1,
Invoermax.nextInt()); // the second input reading
When you enter two int values in a console (any of the kind) you'll see your ending print rows.
If your design was to have a single input, then use cashed value for the second usage
int Invoer = Invoermax.nextInt(); // the first input reading
int Hoogte = ThreadLocalRandom.current().nextInt(1,
Invoer ); // use cashed value

Java - How to print() output to previous line after input

I'm kind of new to Java and I'm still trying to get the hang of it, so I apologize if this is a stupid question, but I was wondering how to print the output on the same line as the input. For example, I'm programming a simple game where the user tries to guess a 4-digit number (rather like Mastermind). I've got the mechanics all figured out, but I'm having a hard time displaying it on the console. In the beginning it might look something like: (a)
Turn Guess Bulls Cows
----------------------------
1
Then, the user would input their guess: (b)
Turn Guess Bulls Cows
----------------------------
1 1234
And as soon as the user hits enter, the program should check their guess against the secret number and output the number of "bulls" (digits in their guess that match the secret number exactly) and "cows" (digits in their guess that are part of the number but in the wrong position), and then start a new line and again await user input. So if the secret number were, say, 4321... (c)
Turn Guess Bulls Cows
----------------------------
1 1234 0 4
2
Trouble is, I can't for the life of me figure out how to get the output to display on the same line as the input. Here's a snippet of what I have so far (stripped-down because the full code is much uglier):
number = "4321";
String guess;
int attempts = 1;
do
{
System.out.print(attempts + "\t\t");
guess = keyboard.next();
attempts++;
int bulls = checkBulls(guess, number);
int cows = checkCows(guess, number);
System.out.print("\t\t" + bulls + "\t\t" + cows + "\n");
}
while (!guess.equals(number));
Which gets me as far as (b), but then when I hit enter, this happens:
Turn Guess Bulls Cows
----------------------------
1 1234 // so far so good
0 4 // ack! These should've been on the previous line!
2
I know this isn't really essential to the game and is probably just me making things more complicated than necessary, but it's driving me nuts. I suppose what's happening is that when you hit enter after typing in your guess, the program starts a new line and then prints the bulls and cows. Is there any way to get around this?

You should look into Ansi Escape Codes.
Something like:
public void update() {
final String guessString = keyboard.next();
System.out.println("\033[1A\033[" + guessString.length() + 'C'
+ "\t{next col}");
}
will result in:
1234 {next col}
(where 1234, followed by {RETURN} was entered by the user; in an appropriately supporting console.
"\033[1A" moves the cursor up 1 row; and "\033[xC" moves the cursor x to the right (where above we calculate x as the length of their guess).
Another option that you have with this approach is to clear the console ("\033[2J") so that you can just completely re-draw the table (which is probably easier to maintain).

Your problem is clear the console or clear a line which depend on the console you are working on and is SO dependend!
See Java Clear Console or Java clear Line
Anyway this example clear the lines and it works on Unix bash shell. (Not in Eclipse console)
It uses "\b" to clear a char ( backslash)
public static void main(String[] args) throws Exception {
int i=0;
while (true)
{
String hello="Good morning"+i;
System.out.print(hello+i);
int j=0;
while(j<=hello.length()){
System.out.print("\b");
j++;
}
i++;
Thread.sleep(1000);
if(i==100)
break;
}
}
The problem in your case is that you need to clear also the new line since you read input and theere is no easy way to read input without new line.
See How to read a single char from the console in Java (as the user types it)?

I know this isn't your implementation but it might suffice. What you can do is print the progress of the game after each input. Then you can see the progress of the game after each attempt and the board will be updated each time.
ArrayList<String> turns = new ArrayList<>();
turns.add("Turn\t\tGuess\t\tBulls\t\tCows\n");
turns.add("----------------------------------------------------");
Scanner keyboard = new Scanner(System.in);
String number = "1234";
String guess = "";
int attempts = 0;
while(!number.equals(guess))
{
for(String line : turns)
System.out.println(line);
System.out.println("Guess the magic number...");
guess = keyboard.nextLine();
attempts++;
int bulls = checkBulls(guess, number);
int cows = checkCows(guess, number);
String attemptOutput = attempts + "\t\t" + guess + "\t\t" + bulls + "\t\t" + cows + "\n";
turns.add(attemptOutput);
}

Here is a different implementation that will achieve the same goal from display perspective but you should note that I am clearing screen by multiple new lines so the final effect is still same i.e. ...
user will enter number under Guess column
each attempt will be displayed immediately after user presses ENTER as you wanted.
NOTE: I have hard-coded bulls and cows value for running the program.
import java.util.ArrayList;
import java.util.Scanner;
public class Game {
public static void main(String[] args) {
ArrayList<String> attempts = new ArrayList<String>();
attempts.add("Turn\t\tGuess\t\tBulls\t\tCows\n");
attempts.add("----------------------------------------------------");
Scanner keyboard = new Scanner(System.in);
String number = "1234";
String guess = "";
int turn = 1;
while (!number.equals(guess)) {
// multiple new lines to clear screen
System.out.println("\n\n\n\n\n\n\n\n");
for (String line : attempts)
System.out.println(line);
System.out.print(turn + "\t\t");
guess = keyboard.nextLine();
// checkbull implementation
int bulls = 0;
// checkcow implementation
int cows = 4;
String attemptOutput = turn + "\t\t" + guess + "\t\t" + bulls
+ "\t\t" + cows;
turn++;
attempts.add(attemptOutput);
}
}
}
Sample Run

Scanner not detecting empty line and Counter not accurate

This should be a very basic program but I'm new to Java. I want to be able to input multiple strings into the console using Scanner to detect them. So far I've been able to get the input part right, I wanted the program to run in such a way that the results are displayed when an empty space is entered as opposed to a string. Strangely enough I've only been able to get results when i hit return twice, however, when there are more than 4 inputs hitting return once works. My counter should count the number of "Courses" entered and display them in the results but it gives inaccurate readings.
import java.util.Scanner;
public class Saturn
{
static Scanner userInput = new Scanner(System.in);
public static void main(String[] args)
{
System.out.println("For each course in your schedule, enter its building");
System.out.println("code [One code per line ending with an empty line]");
String input;
int counter = 0;
while (!(userInput.nextLine()).isEmpty())
{
input = userInput.nextLine();
counter++;
}
System.out.println("Your schedule consits of " + counter + " courses");
}
}

You're calling Scanner#nextLine twice - once in the while loop expression and again in the body of the loop. You can just assign input from the while loop expression. In addition you can use Scanner#hasNextLine to defend against NoSuchElementException occurring:
while (userInput.hasNextLine() &&
!(input = userInput.nextLine()).isEmpty()) {
System.out.println("Course accepted: " + input);
counter++;
}

Java Loop/User Input from Scanner

Making just a simple basketball program where I ask for the home team name, how many games are in the season, and then in a loop ask for the next team game. Basically when I start the do-while loop, it works great, unless the user types in for example, "Ohio State." The out put will then go from "6 games remaining" to "4 games remaining" for example. Usually it will just ask opponent?, then decrement by one game.
How can I fix so that a 2 word basketball team name doesn't decrement twice?
import java.util.Scanner;
public class Basketball2 {
public static void main(String[] args) throws java.io.IOException {
Scanner scanInput = new Scanner(System.in);
String sHomeTeam;
String sAwayTeam;
int iNumGames;
int iGamesLeft = 0;
System.out.println("Enter home team's name: ");
sHomeTeam = scanInput.nextLine();
System.out.println(sHomeTeam);
System.out.println("How many games are in the home team's basketball season?");
iNumGames = scanInput.nextInt();
System.out.println(iNumGames);
//start looping
do {
System.out.println("Enter opponent team's name: ");
sAwayTeam = scanInput.next();
System.out.println(sAwayTeam);
iGamesLeft = --iNumGames;
System.out.println("There are " + iGamesLeft + " games left in the basketball season");
}//end do
while(iGamesLeft > 0);

Replace: sAwayTeam = scanInput.next(); with sAwayTeam = scanInput.nextLine(); The reason it loops twice is because scanInput.next(); only returns one token (e.g. word) at a time. When you enter two words it doesn't need receive more input from the user before continuing a second time because it already has another word to return. Hence the double loop.
You also need to take care of the line of code that calls nextInt(). This works like the next() method, but, instead of a token (word), it scans in just one character as an int. Try this: after iNumGames = scanInput.nextInt(); put scanInput.nextLine(); This should clear scanInput of anything that is making it skip. Note: because of the way that your code is written, this will only read one character. If you need to read more than one character you should use nextLine() and assign its value to an integer.

Whatever is said in the answer given by Donny Schrimsher is correct. All that you have to do now is after getting the number of games in the home team's basketball season i.e.
System.out.println("How many games are in the home team's basketball season?");
iNumGames = scanInput.nextInt();
You have to add
scanInput.nextLine();
This is because after entering the number of games you press enter key (end of line) and nextInt() method takes the number of games and not the end-of-line. This end-of-line is consumed by the nextLine() method which Donny Schrimsher mentioned in the do-while loop. SO to avoid this you add an extra nextLine() method.
Thus it has to be
System.out.println("How many games are in the home team's basketball season?");
iNumGames = scanInput.nextInt();
scanInput.nextLine();
System.out.println(iNumGames);
plus the changes mentioned by Donny Schrimsher.
Thanks

try below code with all exit functionality also.
import java.util.Scanner;
public class Basketball2 {
public static void main(String[] args) throws java.io.IOException {
Scanner scanInput = new Scanner(System.in);
String sHomeTeam;
String sAwayTeam;
int iNumGames;
int iGamesLeft = 0;
System.out.println("Enter home team's name: ");
sHomeTeam = scanInput.nextLine();
System.out.println(sHomeTeam);
System.out
.println("How many games are in the home team's basketball season?");
iNumGames = scanInput.nextInt();
System.out.println(iNumGames);
// start looping
do {
System.out.println("Enter opponent team's name: ");
scanInput = new Scanner(System.in);
sAwayTeam = scanInput.nextLine();
if(!"".equals(sAwayTeam.trim()) && !"exit".equals(sAwayTeam.trim()))
{
System.out.println(sAwayTeam);
iGamesLeft = --iNumGames;
System.out.println("There are " + iGamesLeft+ " games left in the basketball season");
}
}// end do
while (iGamesLeft > 0 && !"exit".equalsIgnoreCase(sAwayTeam));
}
}

Subject: 'Java Loops' with Scanner
The simple Java program I wrote is working perfectly, you can try for yourself...and you also can convert this program easily into 'while loop', 'do - while loop' and 'for - each loop'.
Rafiq,
VA, USA,
Dated: 04/17/2015
//Examples: 'for loop' with Scanner
package com.java_basics;
import java.util.Scanner;
public class ForLoop_Examples_With_Scanner
{
public static void main(String[] args)
{
//Creating instance of Scanner to allows a user's input to read from System.in
Scanner mySC = new Scanner(System.in);
System.out.println("Please, enter the value of 'int i' between '0 and 2' : ");
int i = mySC.nextInt();
System.out.println("Please, enter the value of 'exitPoint' between '10 and 1000' :");
int exitPoint = mySC.nextInt();
System.out.println("Please, enter the value of 'increment' between '1 and 2' :");
int increment = mySC.nextInt();
mySC.close();//Releasing memory to the OS (Operating System) for reuse
System.out.println("Output:\n" + "======");
for(;i<exitPoint ; i=i+increment)//i++==>i=i+1==>i=i+increment
{
System.out.println(i);
}
}
}