Conditionals not working as intended using Java scanner

Question

I'm basically wondering why my conditional statement allows the variable exponent to become 0.0 if a number such as -0.5 is entered by the user. This is my code...

    Scanner num2 = new Scanner(System.in);
    System.out.println("Enter an integer value for n: ");

    int temp = 0;

    if(num2.hasNextInt()) {
        temp = num2.nextInt();
        if(temp >= 1.0 ){
            exponent = temp;
        }
        else {
            System.out.println("You have not entered a positive integer value for n.");
            exponent();
        }
    }
    return exponent;

The weird part occurs when I assign temp to the nextInt. By doing so, I hope to make the following conditional statement work as intended, (temp has to be greater than or equal to 1 for exponent to be set). However, when I call this function and put in -0.5, the function completes and makes exponent = 0. In this case, my goal is to have an exponent that is greater than or equal to 1. Thanks in advance!

BlackDwarf · Accepted Answer · 2014-09-14 19:23:01Z

1

If your input is -0.5, then the condition num2.hasNextInt() will be false, and the next executed instruction will be return exponent;, which seems to be returning 0 here (I don't know why since the code you provided is incomplete).

To check properly if the input is correct, try something like:

if(num2.hasNextInt() && (temp = num2.nextInt()) >= 1) {
    exponent = temp;
}
else {
    System.out.println("You have not entered a positive integer value for n.");
    exponent();
}

EDIT: I didn't know what your exponent() method did, but if it's the same method, I would also recommend using a simple for loop instead of recursive calls, as stated in the other answer.

edited Sep 14, 2014 at 19:23

answered Sep 14, 2014 at 19:15

BlackDwarf

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1 Comment

Steve Over a year ago

Thanks, my exponent method basically returns an integer called Exponent that has to be greater than or equal to one. By placing the argument of >= 1 in the first conditional, like you stated, -0.5 is no longer returning 0.0 as the exponent.

Elliott Frisch · Accepted Answer · 2014-09-14 19:23:49Z

It appears that you are attempting to recursively change the local value temp. You aren't assigning temp = exponent();, but I would recommend you use a basic loop -

int temp = 0;
while (temp < 1) {
    if (num2.hasNextInt()) { // <-- do we have an int?
      temp = num2.nextInt();
    } else if (num2.hasNext()) { // <-- do we have anything?
      System.err.printf("%s is not an int%n", num2.next());
    } else { // <-- no more input! No valid temp ever received. ERROR and exit.
      System.err.println("No more input");
      System.exit(1);
    }
    System.err.flush();
    if(temp >= 1.0 ){
      exponent = temp;
    } else {
      System.out.println("You have not entered a positive integer value for n.");
      // exponent();
    }
}

Which if run with -0.5 outputs

-0.5 is not an int
You have not entered a positive integer value for n.

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