Using ints/doubles and Strings in the same Scanner variable

Question

So I'm new to java programming, coming from Python, and there's a few concepts that I can't quite understand.

I'm writing a program which allows the user to enter as many numbers as they want and the program should output the average of all of the numbers. I used a while loop to loop through the inputs by the user as many times as they wanted, but I needed a way of exiting the loop so that the program could proceed with calculating the average of all of the inputs. I decided that if the user enters an "=" sign instead of a number, then the program would break out of the loop, but since the Scanner variable was looking for a double, and the "=" sign is not a number, I would have to make it a String. But because the Scanner is looking for a double, the program threw an error when it encountered the "=".

How can I get the program to exit the loop when the user types "="? I know I could just allow the user to enter a number that breaks the loop, but if it was a real world program and the user entered a number, it would count that number along with the previous ones when calculating the average. The code I have so far is as follows:

import java.util.Scanner;
// imports the Scanner class

public class Average{
    public static void main(String[] args){
        double num, total = 0, noOfInputs = 0, answer;
        Scanner scanner = new Scanner(System.in);

        while(true){
            System.out.print("Enter number: ");
            //Prompts the user to enter a number

            num = scanner.nextDouble();
            /*Adds the number inputted to the "num" variable. This is the
            source of my problem*/

            if(num.equals("=")){
                break;}
            /*The if statement breaks the loop if a certain character is
            entered*/

            total = total + num;
            //Adds the number inputted to the sum of all previous inputs

            noOfInputs++;
            /*This will be divided by the sum of all of the numbers because
              Number of inputs = Number of numbers*/
        }

        answer = total / noOfInputs;
        System.out.print(answer);

        }
}

Possible duplicate of [How to handle infinite loop caused by invalid input using Scanner](http://stackoverflow.com/questions/3572160/how-to-handle-infinite-loop-caused-by-invalid-input-using-scanner) — Tom, Oct 08 '16 at 22:16

Athamas · Accepted Answer · 2016-10-08T22:30:16.903

2

Several ways to do this.

You could read every number as a string, and then if it is a number, parse it to get the value.

Integer.parseInt(String s)

Or you could check what comes next and read accordingly:

while (scanner.hasNext()) {
                if (sc.hasNextInt()) {
                   int a = scanner.nextInt();
                } else if (scanner.hasNextLong()) {
                   //...
                }
}

Or you could just catch the InputMismatchException, and work from there.

try{
  ...
} catch(InputMismatchException e){
  //check if  '=' ...
}

edited Oct 08 '16 at 22:30

answered Oct 08 '16 at 22:27

Athamas

609
5
16

1

Thanks! I haven't reached error handling in my tutorials yet, so i didnt think of that. Appreciate it! – ConorH99 Oct 08 '16 at 22:28
I think that in your second example code, the while loop won't terminate unless you specify a terminating condition (correct me if I'm wrong, though). So maybe implement the following algorithm: while the scanner has a token and that token converted to a string is not the "=" symbol, keep on getting the nextInt and calculating the average. Otherwise, the while loop will never know when to stop looking for the next token – Aleksandr Hovhannisyan Oct 08 '16 at 22:33
@AleksandrH The example is just meant to show how to check the input, the OP already showed that he knows how to use `break` . – Athamas Oct 08 '16 at 23:06

Using ints/doubles and Strings in the same Scanner variable

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