Question

the instructions are: Enter an integer (32 bit) and sum its digits, you may be given a negative or positive integer. When reading in a negative integer, sum the digits but ignore the – sign.

this is what I have. Somehow I can’t get it to ignore the negative signs when the integer is negative.

import java.util.Scanner;

public class Exercise2_6M {
    public static void main(String[] args) {
        // Create a Scanner
        Scanner input = new Scanner(System.in);

        // Enter amount
        System.out.print("Enter an integer:");
        int integer = input.nextInt();
        if (integer < 0)
            integer = -integer;

        // Calculations
        int rinteger = Math. abs (integer);
        int lastinteger = integer % 10;
        int X = integer / 10;
        int secondinteger= X % 10;
        int firstinteger = X /10;
        int finalinteger = firstinteger + secondinteger + lastinteger;


        // Display results
        System.out.println("Sum all digits in " + rinteger + " is " + finalinteger);
    }
}

Answer 1

To ignore the negative sign:

int integer = Math.abs(input.nextInt());

Edit:
I didn’t notice that your code already did this. To make the code show the negative sign at the end, get rid of the following lines:

if (integer < 0)
        integer = -integer;

since you’re already doing

int rinteger = Math. abs (integer);

Then, replace all instances other than the fist of integer in the calculations sections with rinteger, like this

    // Calculations
    int rinteger = Math. abs (integer);
    int lastinteger = rinteger % 10;
    int X = rinteger / 10;
    int secondinteger= X % 10;
    int firstinteger = X /10;
    int finalinteger = firstinteger + secondinteger + lastinteger;

Finally, when displaying the results, use integer instead of rinteger to restore the minus sign, or just put in a minus sign manually if integer<0.

Your code is also flawed if integer is more than 3 digits, as others have pointed out, but that’s a separate issue.

To add more than 3 digits, you’ll need a loop. Try this:

import java.util.Scanner;
public class Exercise2_6M
{
    public static void main(String[] args) 
    {
        // Create a Scanner
        Scanner input = new Scanner(System.in);

        // Enter amount
        System.out.print("Enter an integer: ");
        int integer = input.nextInt();

        // Calculations
        int rinteger = Math. abs (integer);
        int sum = 0;
        int i=0;

        //loop through each digit (starting from the least significant) until the end of the number
        while(rinteger / Math.pow(10,i) > 0)
        {
            sum+=getDigit(rinteger,i);
            i++;
        }


        // Display results
        System.out.println("Sum all digits in " + integer + " is " + sum);
    }

    public static int getDigit(int num, int power)
    {
        return (num % (int)Math.pow(10,power+1)) / (int)Math.pow(10,power);
    }
}