So translating this into pseudo-code: while correctinput is false: 1. print “Enter age:” 2. set newPerson’s age with input from user 3. ignore new line 4. set correctinput to true 5. if an error such as not a number, print “Age must be a number” and set correctinput to true

You have to move the input.next() inside of the loop and I would recommand to use a while instead of a for loop:

public static void main(String[] args) {

    Scanner input = new Scanner(System.in);
    String secret = "Please", guess = "";

    System.out.print("Secret word?");

    while (!guess.equals(secret)) {
        guess = input.next();

        if (guess.equals(secret)) {
            System.out.println("enter");
        } else {
            System.out.println("try again");
        }
    }
}

Easy with do-while:

Scanner keyboard = new Scanner(System.in);
int startr, endr;
boolean good = false;
do
{
  System.out.println("Enter the Starting Number of the Range: ");
  startr = keyboard.nextInt();
  if(startr % 10 == 0 && startr >= 0)
    good = true;
  else
    System.out.println("Numbers is not divisible by 10");
}
while (!good);

good = false;
do
{
    System.out.println("Enter the Ending Number of the Range: ");
    endr = keyboard.nextInt();
    if(endr % 10 == 0 && endr <= 1000)
      good = true;
    else
      System.out.println("Numbers is not divisible by 10");
}
while (!good);

// do stuff

You are seeing outputs for each input because you call main recursively. If you immediately type a correct int, the flow is this:

main
  ask for input -> int
  print i (1)

But in your case the input is not an int. This is what happens: you type the first input, it fails. You do not print yet because you first call main again, asking for the next input. Only when you get a correct int you print, and then finish and allow the previous main-execution to finish by printing, which then allows the previous... and so on:

main(args)
    ask for input -> a !int
    main(args)
        ask for input -> d !int
        main(args)
            ask for input -> 2.0 !int
            main(args)
                ask for input -> 1 int
                print 1 (1)
            print 0 (2.0)
        print 0 (d)
    print 0 (a)

Look at Ravi's answer for a proper way to repeatedly ask for input without using try/catch (which is discouraged).

but here I want to loop until valid value is entered

Since you want to continuously receive a value until it is valid. It is an obvious hint you need to enclose your prompting of input within your loop:

System.out.println("enter a number");  
int a=sc.nextInt(); 

while(!validateValue(a)){                   //so long value is invalid, repeat.
    System.out.println("enter a number");  
    a=sc.nextInt();                         //prompt for input
}
System.out.println("valid value");

---

But if I were you, I will use a do-while loop, so we do not have to prompt for input twice.

do{                   
    System.out.println("enter a number");  
    a=sc.nextInt();                         
}while(!validateValue(a));
System.out.println("valid value");

Sure, I've also added some comments to hopefully make the code a bit clearer for you. ```java String response = console.readLine("Do you understand do while loops?"); //First prompt the user and store the result to the response String. do { //Start a do loop, do loops run the code in them once, //then repeats it while the condition it has been given is true. response = console.readLine("Do you understand do while loops?"); //Sets the response equal to the prompt again. } while (response.equals("No")); //Here we declare the condition for the do loop to continue. //We are checking if the response variable is equal to the string "No". console.printf("Because you said %s, you passed the test!", response); //Then finally we are printing out a formatted string. //In a formatted string %s is used as placeholder for string variables. //The second argument passed to printf is the first variable we want to pass into the placeholder. ``` Edit: Made some minor changes mainly to clarify some stuff about the do loop.

In your final code example in the class called CalTest where you assign valX = input.nextDouble(); you could a call recursive method that handles the exception until the input is what you want. Something like this:

private static double getNextDouble(Scanner input) {
    try {
        return input.nextDouble();
    } catch (InputMismatchException e) {
        System.out.println("Value X must be a number: ");
        input.next();
        return getNextDouble(input);
    }
}

You'll replace valX = input.nextDouble(); with valX = getNextDouble(input);.

You can tidy this up and make it work for your other potential error cases, perhaps creating a parameter for the output message and passing it in as an argument.

Start by assuming the input is valid (and set valid to true on every iteration of the loop). Only set valid to false when you encounter an exception (hopefully the one you raised).

do {
    valid = true;
    try {
        System.out.println("Enter wall height (feet): ");
        wallHeight = scnr.nextDouble();
        if (wallHeight <= 0) {
            throw new Exception("Invalid Input");
        }
    } catch (Exception e) {
        valid = false;
        System.out.println("Invalid Input");
    }
} while (!valid);

Note that you do not appear to need an exception here, as

do {
    valid = true;
    System.out.println("Enter wall height (feet): ");
    wallHeight = scnr.nextDouble();
    if (wallHeight <= 0) {
        System.out.println("Invalid Input");
        valid = false;
    }
} while (!valid);

would also work. Of course, that assumes the user only inputs valid double(s). If you need handle arbitrary input, you should check that there is a double before you attempt to consume it (and you must consume anything that isn't a double or you have an infinite loop). Like,

do {
    valid = true;
    System.out.println("Enter wall height (feet): ");
    if (scnr.hasNextDouble()) {
        wallHeight = scnr.nextDouble();
        if (wallHeight <= 0) {
            System.out.println("Invalid Input");
            valid = false;
        }
    } else {
        System.out.println("Invalid Input " + scnr.nextLine());
        valid = false;
    }
} while (!valid);

Use a while loop above input line as:

 while(true)

And, use if condition to break.

if(year == 0)
    break;

Also, condition for leap year is wrong in your code. It should be:

if((year % 100 == 0 && year % 400 == 0) || (year % 4 == 0 && year % 100 != 0))
    //its a leap year
else
    //its not

PS: As in comments, I'll give a complete code:

import java.util.*;

public class Task10 {

public static void main(String[] args) {
    System.out.println("Enter a year to check if it is a leap year");
    while(true){
    Scanner input = new Scanner(System.in);
        int year = input.nextInt();
        if(year == 0)
            break;
        if((year % 100 == 0 && year % 400 == 0) || (year % 4 == 0 && year % 100 != 0))
            System.out.println(year + " is a leap year");
        else
            System.out.println(year + " is not a leap year");
    }
}

}