We Keep Coding

How to loop a user input until integer is entered?

I want to run an interactive program where a user is prompted to enter a number of students. If the user inputs a letter or other character besides a whole number, they should be asked again ("Enter the number of students: ")
I have the following code:
public int[] createArrays(Scanner s) {
int size;
System.out.print("Enter the number of students: ");
size = s.nextInt();**
int scores[] = new int[size];
System.out.println("Enter " + size + " scores:");
for (int i = 0; i < size; i++) {
scores[i]=getValidInt(s,"Score " + (i + 1) + ": ");
}
return scores;
}
How can I create a loop for this?

Let's add a loop, take the value as String and check if it is a number:
String sizeString;
int size;
Scanner s = new Scanner(System.in);
do {
System.out.print("Enter the number of students: ");
sizeString = s.nextLine();
} while (!(sizeString.matches("[0-9]+") && sizeString.length() > 0));
size = Integer.parseInt(sizeString);

Try catching the exception and handling it until you get the desired input.
int numberOfStudents;
while(true)
{
try {
System.out.print("Enter the number of student: ");
numberOfStudents = Integer.parseInt(s.next());
break;
}
catch(NumberFormatException e) {
System.out.println("You have not entered an Integer!");
}
}
//Then assign numberOfStudents to the score array
int scores[] = new int[numberOfStudents]

try this
public int[] createArrays(Scanner s) {
int size;
System.out.print("Enter the number of students: ");
while(true) {
try {
size = Integer.parseInt(s.nextLine());
break;
}catch (NumberFormatException e) {
System.out.println();
System.out.println("You have entered wrong number");
System.out.print("Enter again the number of students: ");
continue;
}
}
int scores[] = new int[size];
System.out.println("Enter " + size + " scores:");
for (int i = 0; i < size; i++) {
scores[i]=getValidInt(s,"Score " + (i + 1) + ": ");
}
return scores;
}

int no1 = 0;
Scanner scanner = new Scanner(System.in);
while(true)
{
try {
System.out.print("Number 1: ");
no1 = Integer.parseInt(scanner.next());
break;
}
catch(NumberFormatException e) {
System.out.println("..You have not entered valid value!");
}
}

How am i going to use while loop and if else if user enter the same input twice and it will try again

I want to apply this function in java. Inside while loop, you need to input number of repetition you want to input a number. if you input a number that equals to the number that you enter previously, it will repeat a loop and enter a number again. This code is not finish yet. I hope u understand what i want to achive. thank you
System.out.print("Enter number of times: ");
int times = number.nextInt();
int i = 1;
while ( i <= times){
System.out.print("Enter a number : ");
int input = number.nextInt();
i++;
if( input == input){
System.out.println("It is already taken");
}
}
}
}

Let's use a temp variable to store the value of previous input. If new input is same as previous input, the iterator i should not increase, so we use i--
System.out.print("Enter number of times: ");
int times = number.nextInt();
int i = 1;
int temp=0;
int inputArray[] = new int[times];
while ( i <= times){
System.out.print("Enter a number : ");
int input = number.nextInt();
i++;
if( input == temp){
System.out.println("It is already taken");
i--;
}else {
inputArray[i-2]=input;
}
temp=input;
}
}

The thing with that solution is that is only checks for the number just entered before the current one. I understood that you want to check that the number the user entered is unique and it has to be checked against every number that he/she has entered before.
See the code for that:
import java.util.Scanner;
import java.util.ArrayList;
public class testMe{
public static void main(String[] args){
Scanner scanner = new Scanner(System.in);
System.out.print("Enter number of times: ");
int times = scanner.nextInt();
int i = 0;
ArrayList<Integer> listWithEntries = new ArrayList<Integer>();
while (i < times){
System.out.print("Enter a number : ");
int input = scanner.nextInt();
if(listWithEntries.size() == 0){
listWithEntries.add(input);
i++;
} else {
for(int j = 0; j < listWithEntries.size(); j++){
if(input == listWithEntries.get(j)){
System.out.println("It is already taken!");
break;
}
if(j == listWithEntries.size()-1 && input !=
listWithEntries.get(j)){
listWithEntries.add(input);
i++;
break;
}
}
}
}
}
}

I would like put a optional "wrong number. Try again" when is

I have just started learn java codes, that is why might I have a simple question that is not simple for me.
I would like put a optional "wrong number. Try again" when is entered different number than secretNum. May you guys help me out on this code?
// I need learn how put "try again" when the number is != than guess number.
/* I have tried
* 1)Change the signal "==" or "!=".
* 2) do {
System.out.println("Guess what is the number 0 to 10: ");
if (sc.hasNextInt()) {
guess = sc.nextInt();
}
} while(secretNum != guess);{
System.out.println("Well done");
System.out.println();
System.out.println("Are you ready for the next step?");
System.out.println();
}
*/
import java.util.Scanner;
public class GuessNumber {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("Enter name:");
if(sc.hasNextLine()) {
String userName = sc.nextLine();
System.out.println("Hello " + userName + ",");
System.out.println();
}
int secretNum = 5;
int secretNum2 = 15;
int guess = 0;
do {
System.out.println("Guess what is the number 0 to 10: ");
if (sc.hasNextInt()) {
guess = sc.nextInt();
}
} while(secretNum != guess);{
System.out.println("Well done\n");
System.out.println("Are you ready for the next step?\n");
}
// I need learn how put "try again" when the number is != than guess number.
/* I have tried
* 1)Change the signal "==" or "!=".
* 2) do {
System.out.println("Guess what is the number 0 to 10: ");
if (sc.hasNextInt()) {
guess = sc.nextInt();
}
} while(secretNum != guess);{
System.out.println("Well done");
System.out.println();
System.out.println("Are you ready for the next step?");
System.out.println();
}
*/
System.out.println("Enter Yes or No");
while(!sc.next().equals("yes")&& !sc.next().equals("no"));{
System.out.print("Yes");
}
do {
System.out.println("Guess what is the number 11 to 20: ");
if (sc.hasNextInt()) {
guess = sc.nextInt ();
}
}while(secretNum2 != guess);{
System.out.println("Congratulations");
System.out.println();
System.out.println("The End");
}
}
}
````````

You don't need do{} while() for the checks you want to do here, just while(){} loops would be enough.
Please try this code instead:
import java.util.Scanner;
public class GuessNumber {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("Enter name:");
if (sc.hasNextLine()) {
String userName = sc.nextLine();
System.out.println("Hello " + userName + ",");
System.out.println();
}
int secretNum = 5;
int secretNum2 = 15;
int guess = 0;
System.out.println("Guess what is the number 0 to 10: ");
if (sc.hasNextInt()) {
guess = sc.nextInt();
}
while (secretNum != guess) {
System.out.println("Please try again\n");
if (sc.hasNextInt()) {
guess = sc.nextInt();
}
}
System.out.println("Well done\n");
System.out.println("Are you ready for the next step?\n");
System.out.println("Enter Yes or No");
while (!sc.next().equals("yes") && !sc.next().equals("no"))
{
System.out.print("Yes");
}
System.out.println("Guess what is the number 11 to 20: ");
if (sc.hasNextInt()) {
guess = sc.nextInt();
}
while (secretNum2 != guess) {
System.out.println("Please try again\n");
if (sc.hasNextInt()) {
guess = sc.nextInt();
}
}
System.out.println("Congratulations");
System.out.println();
System.out.println("The End");
}
}

if a user inputs a letter instead of a number tell them it's not a number

I'm making a guessing game, all the code works fine except for that I want them to make a number to guess between, I can't seem to figure out how to make it so that if the user inputs a letter like "d" instead of a number like "15" it will tell them they can't do that.
Code:
import java.util.Scanner;
import java.util.Random;
public class GuessingGame {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
Random rand = new Random();
while (true) {
System.out.print("Pick a number: ");
int number = input.nextInt();
if (number != int) {
System.out.println("That's not a number");
} else if (number == int) {
int random = rand.nextInt(number);
break;
}
}
System.out.println("You have 5 attempts to guess the number or else you fail. Goodluck!");
System.out.println("");
System.out.println("Type 'begin' to Begin!");
System.out.print("");
String start = input.next();
if (start.equals("begin")) {
System.out.print('\f');
for(int i=1; i<6; i++) {
System.out.print("Enter a number between 1-" + number + ": ");
int number = input.nextInt();
if (number > random) {
System.out.println("Too Big");
System.out.println("");
} else if (number < random) {
System.out.println("Too Small");
System.out.println("");
} else if (number == random) {
System.out.print('\f');
System.out.println("Correct!");
break;
}
if (i == 5) {
System.out.print('\f');
System.out.println("You have failed");
System.out.println("Number Was: " + random);
}
}
} else if (start != "begin") {
System.out.print('\f');
System.out.println("Incorrect Command");
System.out.println("Please Exit Console And Retry");
}
}
}

use try catch
for example
try{
int a=sc.nextInt();
}catch(Exception e){
System.out.println("not an integer");
}

You could use nextLine() instead of nextInt() and check the out coming String if it matches() the regular expression [1-9][0-9]* and then parse the line with Integer.valueOf(str).
Like:
String str=input.nextLine();
int i=0;
if(str.matches("[1-9][0-9]*"){
i=Integer.valueOf(str);
} else {
System.out.println("This is not allowed!");
}
I hope it helps.

Do something like this:
Scanner scan = new Scanner(System.in);
while(!scan.hasNextInt()) { //repeat until a number is entered.
scan.next();
System.out.println("Enter number"); //Tell it's not a number.
}
int input = scan.nextInt(); //Get your number here

How to check if user input is String, double or long in Java

I'm a beginner in java. I want to check first if the user input is String or Double or int. If it's String, double or a minus number, the user should be prompted to enter a valid int number　again. Only when the user entered a valid number should then the program jump to try. I've been thinking for hours and I come up with nothing useful.Please help, thank you!
import java.util.InputMismatchException;
import java.util.Scanner;
public class Fizz {
public static void main(String[] args) {
System.out.println("Please enter a number");
Scanner scan = new Scanner(System.in);
try {
Integer i = scan.nextInt();
if (i % 3 == 0 && (i % 5 == 0)) {
System.out.println("FizzBuzz");
} else if (i % 3 == 0) {
System.out.println("Fizz");
} else if (i % 5 == 0) {
System.out.println("Buzz");
} else {
System.out.println(i + "は3と5の倍数ではありません。");
}
} catch (InputMismatchException e) {
System.out.println("");
} finally {
scan.close();
}
}

One simple fix is to read the entire line / user input as a String.
Something like this should work. (Untested code) :
String s=null;
boolean validInput=false;
do{
s= scannerInstance.nextLine();
if(s.matches("\\d+")){// checks if input only contains digits
validInput=true;
}
else{
// invalid input
}
}while(!validInput);

You can also use Integer.parseInt and then check that integer for non negativity. You can catch NumberFormatException if the input is string or a double.
Scanner scan = new Scanner(System.in);
try {
String s = scan.nextLine();
int x = Integer.parseInt(s);
}
catch(NumberFormatException ex)
{
}

Try this one. I used some conditions to indicate the input.
Scanner scan = new Scanner(System.in);
String input = scan.nextLine();
int charCount = input.length();
boolean flag = false;
for(int x=0; x<charCount; x++){
for(int y=0; y<10; y++){
if(input.charAt(x)==Integer.toString(y))
flag = true;
else{
flag = false;
break;
}
}
}
if(flag){
if(scan.hasNextDouble())
System.out.println("Input is Double");
else
System.out.println("Input is Integer");
}
else
System.out.println("Invalid Input. Please Input a number");

Try this. It will prompt for input until an int greater than 0 is entered:
System.out.println("Please enter a number");
try (Scanner scan = new Scanner(System.in)) {
while (scan.hasNext()) {
int number;
if (scan.hasNextInt()) {
number = scan.nextInt();
} else {
System.out.println("Please enter a valid number");
scan.next();
continue;
}
if (number < 0) {
System.out.println("Please enter a number > 0");
continue;
}
//At this stage, the number is an int >= 0
System.out.println("User entered: " + number);
break;
}
}

boolean valid = false;
double n = 0;
String userInput = "";
Scanner input = new Scanner(System.in);
while(!valid){
System.out.println("Enter the number: ");
userInput = input.nextLine();
try{
n = Double.parseDouble(userInput);
valid = true;
}
catch (NumberFormatException ex){
System.out.println("Enter the valid number.");
}
}