This question already has answers here:
How to break a while loop from an if condition inside the while loop?
(3 answers)
Closed 2 years ago.
//File name: SmallIO.java
import java.util.Scanner;
public class SmallIO{
public static void main(String[] args){
Scanner keyboard = new Scanner (System.in);
String a = ""; // initialise to empty string
while (true){
//an infinite loop, use Ctrl-C (from command prompt) to quit
System.out.println("Enter a line:");
a = keyboard.nextLine();
System.out.println("Your line: " + a);
System.out.println();
}//end of while
}//end of main
}//end of class
There are multiple ways, the simplest one would be to use an actual for loop:
for (int i = 1; i <=5; i++) {....}
This is the same as:
int i = 1;
while (i <= 5) {.... i++; }
To break a loop(any loop), you use the break statement.
To break a loop after 5 iterations, you use a counter
This is one of the way to use a counter in combination with break
int counter = 0;
while(true) {
counter++;
if (counter == 5) break;
}
Related
I am a beginner and as you can see I made a simple Java game.
The user has 5 tries to guess a number between 1 and 20.
If the user wins a congratulations message will show.
If the user didn't succeed a game over message will pop up.
Issue
When the user enters the right answer on the 5th try both congratulations and game over messages will pop up.
Code
package org.meicode.Loops;
import java.util.Objects;
import java.util.Random;
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
System.out.println("Welcome");
System.out.println("Enter your name please ");
Scanner scanner = new Scanner(System.in);
String name = scanner.next();
System.out.println("Hello " + name);
System.out.println("Type 1 to start the game");
int yes = scanner.nextInt();
while (yes != 1) {
System.out.println("Type 1 to start the game");
yes = scanner.nextInt();
}
System.out.println("Guess the number in my mind,It is between 1 and 20 and you got 5 tries");
int timestried = 0;
Random random = new Random();
int x = random.nextInt(20) + 1;
while (timestried < 5) {
timestried++;
Scanner scanner1 = new Scanner(System.in);
int answer = scanner.nextInt();
if (x == answer) {
System.out.println("Well done, you did it");
} else if (x > answer) {
System.out.println("Try again,hint:the value is bigger than what you typed");
} else if (x < answer) {
System.out.println("Try again,hint:the value is smaller than what you typed");
}
}
System.out.println("Game over, the number was " + x);
}
}
How can I fix it?
Here is my attempt. I have added some comments in the code to help you.
Note that I have changed some of the file names to, so you may need to change them back for it to run, or just copy the main code section:
package com.misc;
import java.util.Objects;
import java.util.Random;
import java.util.Scanner;
public class GameTest {
public static void main(String[] args) {
System.out.println("Welcome");
System.out.println("Enter your name please ");
Scanner scanner = new Scanner(System.in);
String name = scanner.next();
System.out.println("Hello " + name);
System.out.println("Type 1 to start the game");
int yes = scanner.nextInt();
//We initialize the answer variable here to use it later on.
int answer = 0;
while (yes != 1) {
System.out.println("Type 1 to start the game");
yes = scanner.nextInt();
}
System.out.println("Guess the number in my mind,It is between 1 and 20 and you got 5 tries");
int timestried = 0;
Random random = new Random();
int x = random.nextInt(20) + 1;
//Print out the randomly generated number so we can test it. We answer wrong 4 times then put in the right answer to see if the message is fixed.
System.out.println("Testing: the answer is " + x);
while (timestried < 5) {
timestried++;
Scanner scanner1 = new Scanner(System.in);
answer = scanner.nextInt();
if (x == answer) {
System.out.println("Well done, you did it");
} else if (x > answer) {
System.out.println("Try again,hint:the value is bigger than what you typed");
} else if (x < answer) {
System.out.println("Try again,hint:the value is smaller than what you typed");
}
}
//This is the conditional that uses the answer variable we declared earlier above to avoid printing out the Game Over message in a success scenario.
if (x != answer) {
System.out.println("Game over, the number was " + x);
}
}
}
Here is proof that it works. I made the program print out the real answer, answered wrong 4 times and correctly the 5th time.
Simple fix
There are 2 things I would add to your code to achieve the desired behavior:
break or exit the loop on correct answer
set a flag signaling the question was solved to later build the message upon it
Basics: How to break loops and why
You can achieve this by two ways:
break the loop when the user typed the correct answer
add an exit-condition to the loop
return from the whole method prematurely
throw an exception that can either be caught outside or will also exit the method
I will explain (1) and (2) here in this answer (3) in a separate answer.
(1) Breaking the loop
The loop shall continue until:
the maximum number of tries has been reached
the correct answer was given
Use a break; statement to break the loop if correct answer:
if (x == answer) {
System.out.println("Well done, you did it");
break;
}
Note: contrary a continue; will skip further loop-body and jump to the next iteration.
(2) add a flag signaling premature exit (e.g. correct answer)
You can add a flag that is set to true if the user types the correct answer:
boolean userHasAnsweredCorrect = false;
while (timesTried < 5) { // here the flag can be added instead breaking
if (x == answer) {
System.out.println("Well done, you did it");
userHasAnsweredCorrect = true;
break;
}
}
// omitted some lines .. then at the end
if (userHasAnsweredCorrect) {
System.out.println("You beat the game!")
} else {
System.out.println("Game over, the number was " + x);
}
See how you define the flag before the loop, set it inside the loop (together with a break;) and then test on the flag after the loop.
Combined: set flag and add exit-condition
boolean userHasAnsweredCorrect = false;
while (timesTried < 5 && !userHasAnsweredCorrect) { // here the break happens instead
if (x == answer) {
System.out.println("Well done, you did it");
userHasAnsweredCorrect = true;
// break;
}
}
Find 2 more simpler ways of breaking the loop in my other answer, here follows the 3rd way:
Put the whole game into a method like startGame() and exit from that. Either exit after loop with max-tries has finished or inside the loop (prematurely) if answered guess was correct.
(3) Exiting the loop and method using return
That premature method-exit can be achieved by inserting a return; inside the loop.
public void startGame() {
// rest of preparation
// starting the game-loop
for (int i = 1; i <= maxTries; i++) { // for-i is indexed and safer (no infinite-loop)
// read input
// score or evaluate answer against x
if (x == answer) {
System.out.println("Well done, you did it");
return; // exit the method, not reaching "game-over" after the loop
}
// continue the iteration
}
// game-over (if not previously exited because of victory)
}
To have an exit-condition for the for loop, define int maxTries = 5 either as local variable, class field or constant.
This question already has answers here:
Scanner is skipping nextLine() after using next() or nextFoo()?
(24 answers)
Closed 4 years ago.
this is a program that given in input 5 names and 5 telephone numbers gives in output the names with their numbers in alphabetical order.
the problem is that when I give in input the first name and the first number, then the program jumps to the second "telephone number input" without making me insert the second name.
I hope this makes sense.
also I wouldn't mind any suggestion to make the sorting easier.
this is the code:
import java.util.Arrays;
import java.util.Scanner;
public class RubricaTelefonica {
public static void main(String[] args) {
String names[] = new String[5];
long phone_num[] = new long[5];
Scanner sc = new Scanner(System.in);
for(int i = 0; i < 5; i++) {
System.out.println("Inserisci il nome:");
names[i] = sc.nextLine();
System.out.println("Inserisci il numero di telefono:");
phone_num[i] = sc.nextLong();
}
sc.close();
String names_unsorted[] = names;
Arrays.sort(names);
long sorted_num[] = new long[5];
for(int a = 0; a < 5; a++) {
//sorted cicle
for(int b = 0; b < 5; b++) {
//unsorted cicle
if(names[a] == names_unsorted[b]) {
sorted_num[a] = phone_num[b];
}
}
}
}
}
You misinterpret nextLong(); it simply reads the long value and then the upcoming nextLine() is triggered by the new line entry from the console.
Put an sc.nextLine() after the nextLong() call, or even nicer is to read the phone number as String with nextLine() and then parse a long from it.
This question already has answers here:
How do I compare strings in Java?
(23 answers)
Closed 5 years ago.
When I try to use a while loop it won't follow the conditions I set in the while. Like if I put while s1 != "n") it will continue even if s1 = n. It does the opposite when I try to use while s1 == "y") and it very irritating. I'm trying to make a factorial calculator that prompts the user if they would like to keep going or stop.
Here's the full code:
package factorial;
import java.util.Scanner;
public class Factorial {
public static void main(String[] args) {
int factorial = 1;
int number = 6;
int i = 1;
String s1 = "y";
Scanner keyboard = new Scanner(System.in);
while(s1 != "n") {
System.out.println("Enter an N:");
number = keyboard.nextInt();
while(i <= number) {
factorial *= i;
i++;
}
System.out.println("Factorial = "+factorial);
System.out.println("Would you like to continue? (y/n)");
s1 = keyboard.next();
}
keyboard.close();
System.out.println("Have a nice day!");
}
}
As #Debabrata says use equals for strings, replace:
while(s1 != "n") {
with
while(!s1.equals("n")) {
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public class decisionMaker {
public static void main(String args[]) {
String option[] = new String[10];
// Output
for (int i = 0; i <= 9; i++) {
Scanner input = new Scanner(System.in);
System.out.print("Enter the next option:");
option[i] = input.next();
System.out.println(" ");
}
for (int i = 0; i <= 9; i++) {
System.out.println("option: ");
System.out.println("option[i]+" ");
}
// Output
}
I'm trying to figure out how to add a count to the options, exit and end the program after entering a certain letter or number, and how to create a random output from the user input. I want it to give me one option that I had input at random. Can anyone help me with one or a few of these things. I'm trying to learn to code on my own, and I'm stuck on these.
Randomness
You can generate random numbers using java.util.Random;:
import java.util.Random;
public class SomeClass{
static Random rand = new Random();
public static void main(String args[]){
System.out.println(rand.nextInt());
}
}
About some broken code:
If you want to print out the value of a variable with System.out.println() then you need only type the variable without any quotation marks. The code you've written below will not compile:
System.out.println("option: ");
System.out.println("option[i]+" ");
Assuming that's what you want to do, it should instead be written as:
System.out.println("option: ");
System.out.println(option[i]);
Or even System.out.println("option: \n"+option[i]);
(The escape sequence \n when placed inside of quotation marks just indicates to the console to add a new line.)
Scanner:
Additionally, as nick zoum pointed out, your Scanner object should be initialized outside of the for loop, such as right underneath of the main() method.
Please comment below if you need clarification or if I misunderstood what you were looking for. It was very hard to understand your question.
You could try something like this:
public class DecisionMaker {
public static void main(String[] args) {
// output
Scanner scanner = new Scanner(System.in);
int size = getInt(scanner);
String option[] = new String[size];
for (int index = 0; index < size; index++) {
System.out.print("Enter the next option:");
option[index] = scanner.next();
}
int index = (int) (Math.random() * size);
System.out.println(option[index]);
scanner.close();
// output
}
public static int getInt(Scanner scanner) {
int size = 0;
while (size <= 0) {
if (scanner.hasNext()) {
if (scanner.hasNextInt()) {
size = scanner.nextInt();
}
}
if (size <= 0) {
System.out.println("The input: " + scanner.next() + " is not a valid value.");
}
}
return size;
}
}
How the program works:
The Scanner is initialized in the beginning and there is only
one instance of it.
Then the program will wait until the user inserts a valid number for
the size of options.
The next 5 lines were essentially copied from your code.
Finally we get a random Integer in the range of 0 - (size - 1) and print
the String of the array with that index.
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How can I access a variable from inside a do-while loop in Java?
The code below writes out a value until the value entered is not is between 0 and 10.
Here is my code :
import java.util.Scanner;
public class DoWhileRange {
public static void main(String[] args) {
do{
System.out.println("Enter a number between 0 an 10");
Scanner in = new Scanner(System.in);
int a = in.nextInt();
int total +=0;
}while (a>0 && a<10);
System.out.println("Loop Terminated");
System.out.println("The total is : "+total);
}
}
The loop continues to ask for input so long as the input is between 0 and 10. Once some other number is entered the loop terminates and displays the total of all inputted numbers.
try like (declare the variable a outside the loop):
int a = -1;
do{
System.out.println("Enter a number between 0 an 10");
Scanner in = new Scanner(System.in);
a = in.nextInt();
}while (a>0 && a<10);
To access a variable beyond the loop, you need to declare/initialize it outside of the loop and then change it inside the loop. If the variable in question wasn't an int, I would suggest that you initialize it to null. However, since you can't initialize an int variable to null, you'll have to initialize it to some random value:
import java.util.Scanner;
public class DoWhileRange {
public static void main(String[] args) {
int a = 0; //create it here
do {
System.out.println("Enter a number between 0 an 10");
Scanner in = new Scanner(System.in);
a = in.nextInt();
} while (a>0 && a<10);
System.out.println("Loop Terminated");
// do something with a
}
}
NOTE: If you simply declare the variable before the loop without initializing it (as per #Evginy's answer), you'll be able to access it outside the loop but your compiler will complain that it might not have been initialized.
try this
Scanner in = new Scanner(System.in);
int a;
do {
System.out.println("Enter a number between 0 an 10");
a = in.nextInt();
} while (a > 0 && a < 10);
System.out.println("Loop Terminated");