Logical operators in 'else if' statement

Question

I am trying to learn "if else" statements and I am having trouble with the middle 'if else' part of the script.

package practice;
import java.util.Scanner;
public class Practice {

public static void main(String[] args) {
    // TODO Auto-generated method stub

    Scanner in = new Scanner(System.in);
    System.out.println("enter a number between 1 and 10 ");
    if (!in.hasNextDouble()) {
        String word = in.next();
        System.err.println(word + " is not a number");
    } else if (!(in.nextDouble() > 0) || !(in.nextDouble() <= 10)) {
        Double wrongnumber = in.nextDouble();
        System.err.println(wrongnumber + " is not between 1 and 10");
    } else {
        System.out.println("It works!");
    }
       return;

   }

 }

There are no errors but in the 'else if' block I can't get it to print the err "..... not between 1 and 10", whether or not I put a number between 1 and 10 or higher. It also wont print the "it works!" line anymore when I add the 'else if' block. any suggestions would be much appreciated.

nextDouble, is going to take a new Double everytime it is called. You should call it once and store the value in a variable. Double number = in.nextDouble; — Wesley De Keirsmaeker
– Wesley De Keirsmaeker, Commented Aug 20, 2018 at 13:49

NaN · Accepted Answer · 2018-08-20 13:55:16Z

4

You are caling in.nextDouble() several times in your if else block, so you get something else every time.

if (!(in.nextDouble() > 0) || !(in.nextDouble() <= 10)) {
        Double wrongnumber = in.nextDouble();
        System.err.println(wrongnumber + " is not between 1 and 10");
}

convert it to something like

double next = in.nextDouble();
if (!(next > 0) || !(next <= 10)) {
            Double wrongnumber = next;
            System.err.println(wrongnumber + " is not between 1 and 10");
}

To be logically correct you might switch to Integer instead of Double values.

edited Aug 20, 2018 at 13:55

answered Aug 20, 2018 at 13:42

NaN

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Comments

stanly · Accepted Answer · 2018-08-20 14:26:21Z

2

You call in.hasNextDouble() several times. Each time it scans new number from input so it may cause your issue. You should also consider how you write conditions. I am aware you may just try what's happening there but this kind of condition is hard to read. You can use

(number <= 1) || (number > 10) (remove negations by inverting operators) for example.

answered Aug 20, 2018 at 14:26

stanly

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1 Comment

RevCarl Over a year ago

thank you and i will keep in mind inverting operators

Pochmurnik · Accepted Answer · 2018-08-20 13:42:28Z

1

else if (!(in.nextDouble() > 0) || !(in.nextDouble() <= 10)) {
    Double wrongnumber = in.nextDouble();

I'm not sure but here you operate on 3 different numbers. Before condition, write it to a variable.
Don't compare int with double

answered Aug 20, 2018 at 13:42

Pochmurnik

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3 Comments

user85421 Over a year ago

just a note: actually there is no int in above code, the compiler converts it to double, or just interprets it as such (but it can be a bit confusing). Worse IMO, is the use of Double...

Pochmurnik Over a year ago

So, how to check if a Double variable is smaller than 10? Using x < 10 is better than x < 10.0 ?

user85421 Over a year ago

assuming that x is double, both are the same (compiled code is exactly the same)

Ramindu Samarawickrama · Accepted Answer · 2018-08-20 13:56:55Z

@RevCarl, According what i understand by your code and the description provided, what you want to do is to check whether the input is a number and whether its between 1 to 10. Also you have not clearly said the type of the input you are expecting. I assume it as integer, and the code below will do the task.

import java.util.Scanner;

public class Demo {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.println("Enter a No between 1 to 10");
        String next = input.next();
        Integer i = Integer.parseInt(next);
        if (null == i) {
            System.out.println("Input is not a number");
        } else {
            if (i > 0 && i < 10) {
                System.out.println("It works");
            } else {
                System.out.println("Not Between 1 to 10");
            }
        }
    }
}

Otherwise u can replace the statement String next = input.next(); with Integer i = input.nextInt(); which takes the integer numbers input from the console.

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