I cannot get out of while loop.
I do not why sc.hasNextInt() does not return false after last read number.
Should I use another method or is there a mistake in my code?
public static void main(String[] args) {
// Creating an array by user keyboard input
Scanner sc = new Scanner(System.in);
System.out.println("Length of array: ");
int[] numbers = new int[sc.nextInt()];
System.out.printf("Type in integer elements of array ", numbers.length);
int index = 0;
**while ( sc.hasNextInt()) {**
numbers[index++] = sc.nextInt();
}
// created method for printing arrays
printArray(numbers);
sc.close();
}
Do the following:
Use the input length as the end of the loop.
// Creating an array by user keyboard input
Scanner sc = new Scanner(System.in);
System.out.println("Length of array: ");
int len = sc.nextInt();
int[] numbers = new int[len]; // use len here
System.out.printf("Type in integer elements of array ", numbers.length);
int index = 0;
for (index = 0; index < len; index++) { // and use len here
numbers[index] = sc.nextInt();
}
// created method for printing arrays
printArray(numbers);
sc.close();
And don't close the scanner.
When you are receiving your input from the console, the Scanner hasNextInt() method placed inside a while loop condition will continue to read (meaning the loop will continue), until one of the following happens:
You submit a non-numeric symbol (e.g. a letter).
You submit a so-called "end of file" character, which is a special symbol telling the Scanner to stop reading.
Thus, in your case you cannot have the hasNextInt() inside your while loop condition - I am showing a solution below with a counter variable that you can use.
However, the hasNextInt() method inside a while loop has its practical usage for when reading from a different source than the console - e.g. from a String or a file. Inspired from the examples here, suppose we have:
String s = "Hello World! 3 + 3.0 = 6 ";
We can then pass the string s as an input source to the Scanner (notice that we are not passing System.in to the constructor):
Scanner scanner = new Scanner(s);
Then loop until hasNext(), which checks if there is another token of any type in the input. Inside the loop, perform a check if this token is an int using hasNextInt() and print it, otherwise pass the token to the next one using next():
while (scanner.hasNext()) {
if (scanner.hasNextInt()) {
System.out.println("Found int value: " + scanner.next());
} else {
scanner.next();
}
}
Result:
Found int value: 3
Found int value: 6
In the example above, we cannot use hasNextInt() in the while loop condition itself, because the method returns false on the first non-int character that it finds (so the loop closes immediately, as our String begins with a letter).
However, we could use while (hasNextInt()) to read the list of numbers from a file.
Now, the solution to your problem would be to place the index variable inside the while loop condition:
while (index < numbers.length) {
numbers[index++] = sc.nextInt();
}
Or for clarity`s sake, make a specific counter variable:
int index = 0;
int counter = 0;
while (counter < numbers.length) {
numbers[index++] = sc.nextInt();
counter++;
}
Related
Confused on this exercise, its asking me to create a loop which remembers multiple integers that the user inputted, and prints them out the exact same way. I'm confused on how to print the input without making it a list and not using any methods. I tried making input equal to i, but that doesn't output anything.
public static void main(String[]args) {
Scanner scanner = new Scanner(System.in);
int i = 0;
int i2 = 0;
ArrayList <Integer> name_input = new ArrayList<>();
while(true) {
System.out.print("print number:");
int input = Integer.valueOf(scanner.nextLine());
name_input.add(input);
if (input == -1) {
break;
}
i++;
}
while(i2 < i){
System.out.println(i);
i2++;
}
}
Original question: The exercise template contains a base that reads numbers from the user and adds them to a list. Reading is stopped once the user enters the number -1.
Expand the functionality of the program so that after reading the numbers, it prints all the numbers received from the user. The number used to indicate stopping should not be printed.
So, I am very new at coding but have a college assignment to create a Word Manipulator. I am supposed to get a string and an INT from the user and invert every Nth word, according to the int input.
I am following steps and am stuck with this error at line 38 (the start of my last FOR LOOP). The compiler is giving me an Not an Statement Error in this line but I cant see where I went wrong.
Could someone gimme a light, please?
ps: I am not allowed to use Token or inverse().
import java.util.Scanner;
public class assignment3 {
public static void main(String[] args) {
// BOTH INPUTS WERE TAKEN
Scanner input = new Scanner (System.in);
String stringInput;
int intInput;
System.out.println("Please enter a sentence");
stringInput = input.nextLine();
System.out.println("Please enter an integer from 1 to 10. \n We will invert every word in that position for you!");
intInput = input.nextInt();
int counter = 1;
// ALL CHARS NOW ARE LOWERCASE
String lowerCaseVersion = stringInput.toLowerCase();
// SPLIT THE STRING INTO ARRAY OF WORDS
String [] arrayOfWords = null;
String delimiter = " ";
arrayOfWords = lowerCaseVersion.split(delimiter);
for(int i=0; i< arrayOfWords.length; i++){
System.out.println(arrayOfWords[i]);
// THIS RETURNS AN ARRAY WITH ALL THE WORDS FROM THE INPUT
}
// IF THE INTEGER INPUT IS BIGGER THAN THE STRING.LENGTH, OUTPUT A MESSAGE
// THIS PART IS WORKING BUT I MIGHT WANT TO PUT IT IN A LOOP AND ASK FOR INPUT AGAIN
if (intInput > arrayOfWords.length){
System.out.println("There are not enough words in your sentence!");
}
// NOW I NEED TO REVERSE EVERY NTH WORD BASED ON THE USER INPUT
//THIS IS WHERE THE ERROR OCCURS
for(int i=(intInput-1); i<arrayOfWords.length; (i+intInput)){
char invertedWord[] = new char[arrayOfWords.length()];
for(int i=0; i < arrayOfWords.length();i++){
ch[i]=arrayOfWords.charAt(i);
}
for(int i=s.length()-1;i>=0;i--){
System.out.print(invertedWord[i]);
}
}
}
}
(i+intInput) isn't a statement. That's like saying 12. Perhaps you mean i=i+intInput or i+=intInput which assigns a value to a variable
well, for one thing, i dont see "s" (from s.length()) initiated anywhere in your code.
I'm trying to make a "for" loop in which it asks the user to input 10 numbers and then only print the positives.
Having trouble controlling the amount of inputs. I keep getting infinite inputs until I add a negative number.
import java.util.Scanner;
public class ej1 {
public static void main(String args[]) {
int x;
for (x = 1; x >= 0; ) {
Scanner input = new Scanner(System.in);
System.out.print("Type a number: ");
x = input.nextInt();
}
}
}
From a syntax point of view, you've got several problems with this code.
The statement for (x = 1; x >= 0; ) will always loop, since x will always be larger than 0, specifically because you're not introducing any kind of condition in which you decrement x.
You're redeclaring the scanner over and over again. You should only declare it once, outside of the loop. You can reuse it as many times as you need.
You're going to want to use nextLine() after nextInt() to avoid some weird issues with the scanner.
Alternatively, you could use nextLine() and parse the line with Integer.parseInt.
That said, there are several ways to control this. Using a for loop is one approach, but things get finicky if you want to be sure that you only ever print out ten positive numbers, regardless of how many negative numbers are entered. With that, I propose using a while loop instead:
int i = 0;
Scanner scanner = new Scanner(System.in);
while(i < 10) {
System.out.print("Enter a value: ");
int value = scanner.nextInt();
scanner.nextLine();
if (value > 0) {
System.out.println("\nPositive value: " + value);
i++;
}
}
If you need to only enter in ten values, then move the increment statement outside of the if statement.
i++;
if (value > 0) {
System.out.println("\nPositive value: " + value);
}
As a hint: if you wanted to store the positive values for later reference, then you would have to use some sort of data structure to hold them in - like an array.
int[] positiveValues = new int[10];
You'd only ever add values to this particular array if the value read in was positive, and you could print them at the end all at once:
// at the top, import java.util.Arrays
System.out.println(Arrays.toString(positiveValues));
...or with a loop:
for(int i = 0; i < positiveValues.length; i++) {
System.out.println(positiveValues[i]);
}
Scanner scan = new Scanner(System.in);
int input=-1;
for(int i=0;i<10;i++)
{
input = sc.nextInt();
if(input>0)
System.out.println(input);
}
This is a continuation of a previous question to which i was unable to get an answer. The problem is when i try end the program using the System.exit(0) method with a switch statement and a "End" keyword and case, the code no longer runs as it should, only every second integer input is now read by the computer.
Here is my method that is no longer working:
public static int[] ourGuess() {
int[] guessed = new int[4];
Scanner scan = new Scanner(System.in);
System.out.println("Take your guess:");
switch (scan.nextLine()) {
case "End":
System.exit(0);
break;
}
guess = scan.nextInt();
int mod = 10;
int div = 1;
for (int i = 3; i >= 0; i--) {
int num = (guess % mod) / div;
guessed[i] = num;
div = div * 10;
mod = mod * 10;
}
return guessed;
}
The class is a java implementation of the mastermind game. Thanks for all the help!
You're reading two values from the Scanner.
First you read a value with scan.nextLine(), then you discard that value and read another with scan.nextInt().
You need to save the value read and reuse it:
final String line = scan.nextLine();
if(line.equals("End")) {
return guessed;
}
final int guessed = Integer.parseInt(line);
You also shouldn't call System.exit.
First of all, you should not use a switch statement for one case. Also, if the line read is not "End" but an int, you are skipping that one. Try:
String next = scan.nextLine();
if(next.equalsIgnoreCase("End")) System.exit(0);
Then check to see if next is the actual int that was guessed, otherwise read the next int.
By calling nextLine() and nextInt(), you are reading two things from the stream. Instead, cache the value of the nextLine():
String line = scan.nextLine();
switch (line) { ...}
then use that in the following way:
guess = Integer.parseInt(line);
in one line from the standard input I have 3 types of integers: the first integer is id, the second integer is N - some number, and after that follows N integers, separeted by a single space which I want to store in array or ArrayList. How can I do this using BufferedReader? I have the following code:
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String[] line = br.readLine().split(" ");
int ID = Integer.parseInt(line[0]);
int N = Integer.parseInt(line[1]);
My question is is there any elegant way to read the rest of the line and to store it into array?
Use Scanner and method hasNextInt()
Scanner scanner = new Scanner(System.in);
while (scanner.hasNext()) {
if (scanner.hasNextInt()) {
arr[i]=scanner.nextInt();
i++;
}
}
How can I do this using BufferedReader?
You've already read/split the line, so you can just loop over the rest of the inputted integers and add them to an array:
int[] array = new int[N]; // rest of the input
assert line.length + 2 == N; // or some other equivalent check
for (int i = 0; i < N; i++)
array[i] = Integer.parseInt(line[i + 2]);
This will also let you handle errors within the loop (I'll leave that part to you, should you find it necessary).