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How can I handle input string, during the process of if, else if, else including Integer.parseInt?

I would like to handle this situation about inputting wrong string, but error keeps happening because of the else if argument.
Tried try, catch but don't know how to apply it to this code.
import java.util.Scanner;
public class game
{
public static void main(String[] args) {
System.out.println("let's start the multiplication game.");
System.out.println("which times table do you want to choose?");
System.out.println("if you want to do it by your choice, please input number among 2~9. Or if you want to do it randomly, please input number 0");
System.out.println("press \"q\" if you want to quit");
System.out.println("==>");
String input;
Scanner s = new Scanner(System.in);
input = s.nextLine();
int answer;
int multiplier = (int)(Math.random()*8+2);
int random = (int)(Math.random()*8+2);
if (input.equals("q"))
{
System.out.print("quit the game.");
}
else if (Integer.parseInt(input) == 0)
{
System.out.println(random+"times table has been made automatically.");
System.out.print(random+" X "+multiplier+" = "+"? input your answer ==> ");
answer = s.nextInt();
if (answer == random*multiplier)
{
System.out.print("You're right!");
}
else
{
System.out.print("Wrong! The right answer is "+random*multiplier+".");
}
}
else if (Integer.parseInt(input)>=2 && Integer.parseInt(input)<=9)
{
int number = Integer.parseInt(input);
System.out.println("You chose"+number+" times table.");
System.out.print(number+" X "+multiplier+" = "+"? input your answer ==> ");
answer = s.nextInt();
if (answer == number*multiplier)
{
System.out.print("You're right!");
}
else
{
System.out.print("Wrong! The right answer is "+number*multiplier+".");
}
}
else
{
System.out.print("Error. Please try again.");
}
}
}
I expect the result from the else block, but when I input wrong string like "c" or "f" and etc, number format exception error: For input string: "c" (or "f" and etc) happens. Thanks for reading this, and hope you solve this problem.

int check = 0;
try{
check = Integer.parseInt(input);
}catch(NumberFormatException e){
System.out.println("Wrong input");
continue;
}
If you loop this input processing,if it enters catch,you may take input again or you can do what you want when invalid input is entered.If there is no exception,check is your input value,then you can use it in your if and else-if statements like
if(check>0){
...
}

Before Else blocks, you can parse the input like this:
if (input.equals("q")) {
System.out.print("quit the game.");
return;
}
int parsedInput = 0;
try {
parsedInput = Integer.parseInt(input);
} catch (NumberFormatException ex) {
System.out.print("Error. Please try again.");
return;
}
Then you can write if-else for integer input like below:
if (parsedInput == 0) { ... }
else if (parsedInput >= 2 && parsedInput <= 9) {...}
Last else is not needed because I moved it to catch block.

try this it can handle exception
import java.util.Scanner;
public class Game {
public static void main(String[] args) {
System.out.println("let's start the multiplication game.");
System.out.println("which times table do you want to choose?");
System.out.println(
"if you want to do it by your choice, please input number among 2~9. Or if you want to do it randomly, please input number 0");
System.out.println("press \"q\" if you want to quit");
System.out.println("==>");
String input;
Scanner s = new Scanner(System.in);
input = s.nextLine();
int answer;
int multiplier = (int) (Math.random() * 8 + 2);
int random = (int) (Math.random() * 8 + 2);
if (input.equals("q")) {
System.out.print("quit the game.");
}
try {
int check_input = Integer.parseInt(input);
if (check_input == 0) {
System.out.println(random + "times table has been made automatically.");
System.out.print(random + " X " + multiplier + " = " + "? input your answer ==> ");
answer = s.nextInt();
if (answer == random * multiplier) {
System.out.print("You're right!");
} else {
System.out.print("Wrong! The right answer is " + random * multiplier + ".");
}
} else if (check_input >= 2 && check_input <= 9) {
int number = Integer.parseInt(input);
System.out.println("You chose" + number + " times table.");
System.out.print(number + " X " + multiplier + " = " + "? input your answer ==> ");
answer = s.nextInt();
if (answer == number * multiplier) {
System.out.print("You're right!");
} else {
System.out.print("Wrong! The right answer is " + number * multiplier + ".");
}
}
else {
System.out.print("Error. Please try again.");
}
} catch (Exception e) {
System.out.print("Error. Please try again.");
}
}
}

You just need to check the user provided input is number or not. Before parsing it.
I have added new isNumberic method which is returning boolean flag depending user's input and verify it.
public class Game {
public static void main(String[] args) {
System.out.println("let's start the multiplication game.");
System.out.println("which times table do you want to choose?");
System.out.println(
"if you want to do it by your choice, please input number among 2~9. Or if you want to do it randomly, please input number 0");
System.out.println("press \"q\" if you want to quit");
System.out.println("==>");
String input;
Scanner s = new Scanner(System.in);
input = s.nextLine();
int answer;
int multiplier = (int) (Math.random() * 8 + 2);
int random = (int) (Math.random() * 8 + 2);
Game game = new Game();
boolean isvalid = game.isNumeric(input);
if (input.equals("q")) {
System.out.print("quit the game.");
}
else if (isvalid && Integer.parseInt(input) == 0) {
System.out.println(random + "times table has been made automatically.");
System.out.print(random + " X " + multiplier + " = " + "? input your answer ==> ");
answer = s.nextInt();
if (answer == random * multiplier) {
System.out.print("You're right!");
} else {
System.out.print("Wrong! The right answer is " + random * multiplier + ".");
}
}
else if (isvalid && Integer.parseInt(input) >= 2 && Integer.parseInt(input) <= 9) {
int number = Integer.parseInt(input);
System.out.println("You chose" + number + " times table.");
System.out.print(number + " X " + multiplier + " = " + "? input your answer ==> ");
answer = s.nextInt();
if (answer == number * multiplier) {
System.out.print("You're right!");
} else {
System.out.print("Wrong! The right answer is " + number * multiplier + ".");
}
}
else {
System.out.print("Error. Please try again.");
}
}
public static boolean isNumeric(String str)
{
for (char c : str.toCharArray())
{
if (!Character.isDigit(c)) return false;
}
return true;
}
}

You can't send values like a , b, c etc for
Integer.parseInt(String s)
https://docs.oracle.com/javase/7/docs/api/java/lang/Integer.html#parseInt(java.lang.String)
I have try catch block to catch numberformat exception with message to enter valid integer
public static void main(String args[]) {
System.out.println("let's start the multiplication game.");
System.out.println("which times table do you want to choose?");
System.out.println("if you want to do it by your choice, please input number among 2~9. Or if you want to do it randomly, please input number 0");
System.out.println("press \"q\" if you want to quit");
System.out.println("==>");
String input;
Scanner s = new Scanner(System.in);
input = s.nextLine();
int answer;
int multiplier = (int)(Math.random()*8+2);
int random = (int)(Math.random()*8+2);
try {
if (input.equals("q"))
{
System.out.print("quit the game.");
}
else if (Integer.parseInt(input) == 0)
{
System.out.println(random+"times table has been made automatically.");
System.out.print(random+" X "+multiplier+" = "+"? input your answer ==> ");
answer = s.nextInt();
if (answer == random*multiplier)
{
System.out.print("You're right!");
}
else
{
System.out.print("Wrong! The right answer is "+random*multiplier+".");
}
}
else if (Integer.parseInt(input)>=2 && Integer.parseInt(input)<=9)
{
int number = Integer.parseInt(input);
System.out.println("You chose"+number+" times table.");
System.out.print(number+" X "+multiplier+" = "+"? input your answer ==> ");
answer = s.nextInt();
if (answer == number*multiplier)
{
System.out.print("You're right!");
}
else
{
System.out.print("Wrong! The right answer is "+number*multiplier+".");
}
}
else
{
System.out.print("Error. Please try again.");
}
}
catch (NumberFormatException e ) {
System.out.print("pleae enter Valid integer");
}

It's obvious that you are getting this error because you are calling Integer.parseInt on a string variable which doesn't contain an Integer. What you should be doing is putting a check once you get the input to check if the string contains what you need. Something like below
while (true)
{
// Check that the input is between 0 and 9 or q.
if (!((input.charAt(0) >= '0' && input.charAt(0) <= '9') || input.charAt(0) == 'q'))
{
// If it is not, ask for input again.
System.out.println("Input is not correct. If you want to do it by your choice, please input number among 2~9. Or if you want to do it randomly, please input number 0");
input = s.nextLine();
}
else {
// If input is correct, break this look.
break;
}
}
Below is the whole code
public class game
{
public static void main(String[] args)
{
System.out.println("let's start the multiplication game.");
System.out.println("which times table do you want to choose?");
System.out.println("if you want to do it by your choice, please input number among 2~9. Or if you want to do it randomly, please input number 0");
System.out.println("press \"q\" if you want to quit");
System.out.println("==>");
String input;
Scanner s = new Scanner(System.in);
input = s.nextLine();
while (true)
{
if (!((input.charAt(0) >= '0' && input.charAt(0) <= '9') || input.charAt(0) == 'q'))
{
System.out.println("Input is not correct. If you want to do it by your choice, please input number among 2~9. Or if you want to do it randomly, please input number 0");
input = s.nextLine();
}
else {
break;
}
}
int answer;
int multiplier = (int) (Math.random() * 8 + 2);
int random = (int) (Math.random() * 8 + 2);
if (input.equals("q"))
{
System.out.print("quit the game.");
}
else if (Integer.parseInt(input) == 0)
{
System.out.println(random + "times table has been made automatically.");
System.out.print(random + " X " + multiplier + " = " + "? input your answer ==> ");
answer = s.nextInt();
if (answer == random * multiplier)
{
System.out.print("You're right!");
}
else
{
System.out.print("Wrong! The right answer is " + random * multiplier + ".");
}
}
else if (Integer.parseInt(input) >= 2 && Integer.parseInt(input) <= 9)
{
int number = Integer.parseInt(input);
System.out.println("You chose" + number + " times table.");
System.out.print(number + " X " + multiplier + " = " + "? input your answer ==> ");
answer = s.nextInt();
if (answer == number * multiplier)
{
System.out.print("You're right!");
}
else
{
System.out.print("Wrong! The right answer is " + number * multiplier + ".");
}
}
else
{
System.out.print("Error. Please try again.");
}
}
}

Verify input in two separate if/else blocks. Add this code to your "else" statement to catch strings other than "q".
else{
try {
int inputNumber = Integer.parseInt(input);
if(inputNumber == 0) {
// code..
} else if (inputNumber >= 2 && inputNumber <= 9) {
// code..
}
} catch(java.lang.NumberFormatException e) {
System.out.print("Error. Please try again.");
}
}

why don't use try catch?
if (input.equals("q")) {
System.out.print("quit the game.");
}
try {
Integer i = Integer.parseInt(input);
}catch (NumberFormatException e){
System.out.print("Error. Please try again.");
return;
}

Quitting while program is running when user presses 'q' then 'ENTER'

I want to give the user a choice to quit the program while the program is running whenever they feel like it. E.g. Press Q and ENTER at anytime to quit and end program.
I have a try and catch method but whenever I press Q and ENTER, it just displays whats in the catch part.
Here is the code:
public static void partB() {
//Code for partB goes here.
//Continues on with partA but with few changes
/* The number of multiplication problems should not be fixed. Instead,
the program should keep posing new multiplication problems until the user decides to quit by entering the letter "q".
The program should be able to deal with invalid input by the user.
It should ignore such input and restate the current multiplication problem.
*/
//Uses the imported Random function.
Random num = new Random();
//Initialises the minimum and maximum numbers.
int minNumber = 10; //Minimum number to start random
int maxNumber = 20; //Maximum number to start random
int counter = 0; //Counts the number of questions answered.
int correctAnswers = 0; //Counts the number of correct answers given.
final int numberOfQuestions = 0;
while(numberOfQuestions >= 0) {
//Generates a random integer between 10 and 20.
int randInt1 = (num.nextInt(maxNumber - minNumber) + minNumber);
//Repeats for the 2nd integer to get the product of the two numbers.
int randInt2 = (num.nextInt(maxNumber - minNumber) + minNumber);
//Initialise the Scanner function.
Scanner input = new Scanner(System.in);
//Output the Question.
System.out.println("What is " + randInt1 + " X " + randInt2 + "?" + " " + "(Press 'q' and ENTER to quit)");
//Waits for user input.
try {
int userInput = input.nextInt();
String quit = input.nextLine();
//If user input is 'q', quit program.
if(quit.equalsIgnoreCase("q")) {
System.out.println("Exiting...");
System.exit(0);
} else {
int answer = randInt1 * randInt2;
//Checks if the users input is correct.
if (answer == userInput) {
System.out.println("That is correct!");
correctAnswers++;
}
else {
System.out.println("That is incorrect! " + "The correct answer should be " + answer);
counter++;
}
}
} catch(InputMismatchException e) {
System.out.println("You have entered something other than an integer or 'q'! Please try again with a different question!");
}
}
}

If you want to accept both a number and a letter, it is better to use nextLine(). First you check for q, and then parse to number, as follows (note that parseInt will throw a NumberFormatException):
try {
String userInput = input.nextLine();
// If user input is 'q', quit program.
if (userInput.equalsIgnoreCase("q")) {
System.out.println("Exiting...");
System.exit(0);
} else {
int userAnswer = Integer.parseInt(userInput);
int answer = randInt1 * randInt2;
// Checks if the users input is correct.
if (answer == userAnswer) {
System.out.println("That is correct!");
correctAnswers++;
} else {
System.out.println("That is incorrect! " + "The correct answer should be " + answer);
counter++;
}
}
} catch (NumberFormatException e) {
System.out.println(
"You have entered something other than an integer or 'q'! Please try again with a different question!");
}

Basic Java program tune up assistance

My program asks the user for their name, then asks for a number of shuffles of 3 random numbers.
When one of the shuffles adds to the desired number (which is 31) the shuffle stops. I need to happen that the program only reads the LAST SHUFFLE. E.g.
how many shuffles do you want: 3
10 + 11 + 10 = 31 congrats you are the winner!!
The current output is:
9 + 6 + 8
8 + 10 + 12
7 + 9 + 11
I need assistance in making sure the user cannot put non alphabetical characters in their name. I also need the ability to be able to print out how many shuffles the user had before the numbers were printed out.
Here is my code,
`import java.util.InputMismatchException;
import java.util.Scanner;
import java.io.IOException;
import java.util.Random;
public class StringVariables {
public static void main(String[] args) throws NumberFormatException,
IOException {
// user inputs their name in this section
Scanner user_input = new Scanner(System.in);
//enter their first name
String first_name;
System.out.print("Enter Your First Name: ");
first_name = user_input.next();
//enter their last name
String last_name;
System.out.print("Enter Your Last Name: ");
last_name = user_input.next();
//full name printed together
String full_name;
full_name = first_name + " " + last_name;
System.out.println(full_name + " Is Now Playing");
// this is the shuffle portion as well as something to see if a number
int numShuffles = -1;
while (numShuffles < 0) {
System.out.println("How many times do you want the numbers shuffled? ");
try {
numShuffles = user_input.nextInt();
} catch (InputMismatchException inputException) {
System.out.print("Please enter a valid number. \n");
//this is the buffer that resets if the user types a letter instead of a number, or any other character
user_input.next();
}
}
// here is going to be the loop for shuffles
// we are now going to generate their random number and add a delay
// after completing their name fields
delay(3000);
System.out
.println(" You will be given a hand of 3 random numbers between 7-13"
+ "\n you will be drawn a the number of shuffles as you entered above ");
delay(2000);
System.out
.println(" Then, the computer will add the random numbers and if it is equal to 31, you win.");
/*
* end of explanation of the game, next i will create a new screen with
* the user's name and numbers
*/
delay(4000);
// printing 25 blank lines
for (int i = 0; i < 25; i++)
System.out.println(" ");
System.out.println("User playing: " + full_name);
System.out.println("Your lucky numbers are...");
// random number generator
Random random = new Random();
while (true) {
// the shuffle loop
boolean isWinner = false;
for (int i = 0; i < numShuffles; i++) {
int num1 = 7 + random.nextInt(7);
int num2 = 7 + random.nextInt(7);
int num3 = 7 + random.nextInt(7);
System.out.println(num1 + " + " + num2 + " + " + num3 + " = "
+ (num1 + num2 + num3));
// adding the numbers together
if (num1 + num2 + num3 == 31) {
isWinner = true;
System.out
.println("Congratulations !! You are the Lucky Winner !!!!");
break;
//if you loose every shuffle
}
}
if (!isWinner)
System.out.println("Better Luck Next Time");
// play again prompt
System.out
.println(" Do you want to play again? (If you do enter y or yes) \n To exit press any other key ");
String input = user_input.next();
if (!"y".equalsIgnoreCase(input) && !"yes".equalsIgnoreCase(input)) {
break;
}
}
// if pressed y or yes the program will run again with the same number of shuffles entered from before
user_input.close();
}
// delay field
public static void delay(int millis) {
try {
Thread.sleep(millis);
} catch (InterruptedException exp) {
// delay field
}
}
}`

Arraylist numberStore = new Arraylist();
for (int i = 0; i < numShuffles; i++) {
int num1 = 7 + random.nextInt(7);
int num2 = 7 + random.nextInt(7);
int num3 = 7 + random.nextInt(7);
System.out.println(num1 + " + " + num2 + " + " + num3 + " = " + (num1 + num2 + num3));
numberStore.add(num1 + num2 + num3);
}
int lastNumber = (numberStore.size() - 1);
if (lastNumber == 31) {
isWinner = true;
System.out
.println("Congratulations !! You are the Lucky Winner !!!!");
break;
//if you loose every shuffle
}
to make sure that only the last shuffle can get read as a winner or loser.
Because you are initializing your num1, num 2... variables inside of your for loop then those variables are scoped to that for loop. I would suggest that if you want to make sure that only one set of numbers can be judged then you move the scope out of the loop. Adding the totals to an array would then allow you to choose as many as you want to judge.
When it comes to sterilizing your inputs you can use util.Scanner to do most of it for you with a little knowledge of regex:
while (!scan.hasNext("[A-Za-z]+")) {
System.out.println("Nope, that's not it!");
sc.next();
}
This will stop your scanner allowing any none alphabetical char's being entered, you can read more about Regex with this tool

How to randomly position a variable within X + Y = Z operation and loop

I basically want to be able to loop an X + Y = Z equation until the user inputs something other than an integer, like the letter "A" and also when having any number make the loop stop displaying a message.
Also, I am confused on how to randomly position the "?" which the user must input the correct answer.
For example
System.out.println("What is: " + num1 + " + ? = " + answer);
So far:
I am positioning the "?" manually through the IF statements. Can this be done in a more efficient way?
public static void main(String[] args) {
Random rand = new Random();
Scanner input = new Scanner(System.in);
int num1, num2, number3, answer;
do {
num1= 1 + rand.nextInt(10);
num2= 1 + rand.nextInt(10);
answer= num1 + num2;
System.out.println("What is: " + num1 + " + ? = " + answer);
number3= input.nextInt();
if (number3 == num2)
System.out.println("That is correct");
else
System.out.println("That is wrong");
num1= 1 + rand.nextInt(10);
num2= 1 + rand.nextInt(10);
answer= num1 + num2;
System.out.println(num1 + " + ? = " + answer);
number3= input.nextInt();
} while(number3 !=0);
}

Here is one way to do it:
public static void main(String[] args) {
Random rand = new Random();
Scanner scanner = new Scanner(System.in);
int[] xyz = new int[3];
String[] display = new String[3];
int answer, position;
do {
xyz[0] = 1 + rand.nextInt(10);
xyz[1] = 1 + rand.nextInt(10);
xyz[2] = xyz[0] + xyz[1];
for (int i = 0; i < xyz.length; i++)
display[i] = String.valueOf(xyz[i]);
position = rand.nextInt(3);
display[position] = "?";
System.out.println("What is: " + display[0] + " + " + display[1] + " = " + display[2]);
do {
System.out.println("Please enter an integer or 'S' to stop");
String input = scanner.nextLine();
if (input.equals("S")) {
scanner.close();
System.out.println("Stopped");
return;
}
else if (input.matches("\\d+")) { // \\d+ means "a digit (0-9) once or more
answer = Integer.parseInt(input);
break;
}
} while (true);
if (answer == xyz[position])
System.out.println("That is correct");
else
System.out.println("That is wrong");
} while (true);
}
Notes:
I use an inner do-while loop to repeatedly check the input and ask the user for a valid input.
I use 2 arrays: one for storing the numbers and another for storing the display values.
I also added a stop condition since the outer loop is infinite. Always close the Scanner when you finish.
I randomly pick 1 of 3 positions for the "?".

Guessing number using lower,higher,correct options in java

I'm trying to write a java code in java that has following output.
---JGRASP exez: java Guess
Is the number 50? H
Ia the number 75? L
Is the number 62? L
Is the number 56? L
Is the number 53? L
Is the number 51? C
It took me 6 guesses!
---JGRASP: operation complete.
As you see it always cuts range in half.I spent hours trying to figure it out without results.I would really appreciate if you could at least give a hint.Here's my unsuccessful attempt to write the code.
import java.util.Scanner;
public class GuessNumber
{
public static void main(String[]args)
{
int num1 = 0,num2 = 100,guesses = 0;
String answer;
boolean correct = false;
Scanner keyboard = new Scanner(System.in);
do{
System.out.print("Is the number " + <?> + "? "); //have no idea
answer = keyboard.next();
if(answer.equalsIgnoreCase("C")) {
correct = true;
guessses++;
}
else if(answer.equalsIgnoreCase("H")){
? = (num1 + num2) / 2; //lost here
guesses++;
}
else if(answer.equalsIgnoreCase("L")){
? = (num1 + num2) / 2; //lost here
guesses++;
}
}while(correct == false);
System.out.print("It took me " + guesses + " guesses!");
}
}

public static void main(String[]args)
{
Random randomNumber = new Random();
int num1 = 0,num2 = 100,guesses = 0, guess=0;
String answer;
boolean correct = false;
Scanner keyboard = new Scanner(System.in);
do{
guess=randomNumber.nextInt(num2-num1) + num1;
System.out.print("Is the number " + guess + "? ");
answer = keyboard.next();
if(answer.equalsIgnoreCase("C")) {
correct = true;
guessses++;
}
else if(answer.equalsIgnoreCase("H")){
num1 = guess;
guesses++;
}
else if(answer.equalsIgnoreCase("L")){
num2 = guess;
guesses++;
}
}while(correct == false);
System.out.print("It took me " + guesses + " guesses!");
}

Try this, what it does is that, while the answer is not correct, It will take in num1(the min value for the guess) and num2(the max value for the guess) and find their average. If the number is higher than the latest guess, we set the lower bound to the latest guess, if it's lower, we set the upper bound to the latest guess.
import java.util.Scanner;
public class GuessNumber{
public static void main(String[]args)
{
int num1 = 0,num2 = 101,guesses = 0, guess=0;
String answer;
boolean correct = false;
Scanner keyboard = new Scanner(System.in);
do{
guess=(num1+num2) /2 > 0? (num1+num2) /2:1;
System.out.print("Is the number " + guess + "? ");
answer = keyboard.next();
if(answer.equalsIgnoreCase("C")) {
correct = true;
guesses++;
}
else if(answer.equalsIgnoreCase("H")){
num1 = guess;
guesses++;
}
else if(answer.equalsIgnoreCase("L")){
num2 = guess;
guesses++;
}
}while(correct == false);
System.out.print("It took me " + guesses + " guesses!");
}
}