using a "char" sentinel value for "int" input

[jh7468]

If you're writing code that is asking for integer input, but need a sentinel value that is not an integer (i.e., "please enter a number or x to exit"), how would you do it?

Thanks:o

[quad64bit]

All input from the terminal/gui is as a String. So, you could read the string and cast/parse to convert to a different data type.

[jh7468]

Even from a command window?

[Junky]

Yes.

If you use a Scanner and the nextInt method, it just hides that fact that it reads a String and calls the Integer.parseInt method.

[jh7468]

Here is the code -

import java.util.Scanner;

public class W1
{
public static void main(String[] args)
{

int number;
Scanner keyboard = new Scanner(System.in);

System.out.println("enter a number or \"n\" to end");
number = keyboard.nextInt();

while (number != 'n')
{
System.out.println("hello");
System.out.println("enter a number or 'n' to end");
number = keyboard.nextInt();
}

System.out.println("bye");
}
}

If I put in a number, the loop works fine. When I put in anything other than a number, it just crashes.

[Junky]

Because n is not an int so if you enter that the nextInt method will throw an exception. The advice given above may not have been clear. Get user input as a String. Check if that String is "n". If it isn't convert String to int.

[jh7468]

import java.util.Scanner;

public class W1
{
public static void main(String[] args)
{

String number;
String input;
Scanner keyboard = new Scanner(System.in);

System.out.println("enter a number or \"n\" to end");
number = keyboard.nextLine();

while (number != "n")
{
System.out.println("hello");
System.out.println("enter a number or 'n' to end");
number = keyboard.nextLine();
}

System.out.println("bye");
}
}

[Junky]

Do not compare Strings or objects using == or !=, use the equals method instead.

if(str1.equals(str2))

if( ! str1.equals(str2))

[jh7468]

A million thanks. It works.

One day, I hope to give back as much as I have received on this site.

Thanks again.