Java-Code

package pQuersumme;

import java.util.Scanner;

public class Testclass {

	public static void main(String[] args) {
		int input=0;
		Scanner theScanner=new Scanner(System.in);
		System.out.println("Bitte Zahl eingeben:");
		input=theScanner.nextInt();
		System.out.println("Die Quersumme der Zahl: "+input+" lautet "+Testclass.caluclateDigitSum(input));
		
	}

	//Calculate the digit sum of numbers smaller than 100
	static int calculateDigigtSumSimple(int input){
		int digit_sum=0;
		if (input<10) {
			digit_sum=input;
		}else {
			digit_sum=(input/10)+(input%10);
		}
		return digit_sum;
	}

	//Calculates the digits of a number for numbers smaller than 10^1000
	static int calculateDigits(int input){
		int digits=0;
		for (int i = 0; i < 1000; i++) {
			int compareToInput=(int) Math.pow(10, i);
			if (compareToInput>input) {
				digits=i;
				break;
			}
		}
		return digits;
	}
	//Calculate the digit sum of numbers greater than 99
	static int caluclateDigitSum(int input){
		int digit_sum=0;
		int digits=Testclass.calculateDigits(input);
		for (int i = digits-1; i >= 0; i--) {
			digit_sum=(int) (input/Math.pow(10, i))+digit_sum;
			input=(int) (input%Math.pow(10, i));
		}
		return digit_sum;
	}
}

Java-Code

import java.util.Scanner;

public class CrossSum {

	private static Scanner scanner;
	static long input;
	static long sum;

	public static void main(String[] args) {
		System.out.println("Please insert the long you want to sum up: ");
		while (true) {
			scanner = new Scanner(System.in);
			input = scanner.nextLong();
			while (input > 0) {
				sum = sum + input % 10;
				input = input / 10;
			}
			System.out.println("Cross sum = " + sum + "\n");
			sum = 0;
		}
	}
}

Java-Code

        
package digitsum;
import java.util.Scanner;
public class DigitSum {
    public static void main(String[] args) {
        Scanner scr = new Scanner(System.in);
        
        int z = 0;
        for(int i=0; i<=99; i++)
        {
            z += GetDigitSum(i);
        }
        System.out.println(z + " Ist die Quersumme aller Zahlen von 1 - 99. Wenn du die Quersumme einer eigenen Zahl haben willst, gib sie jetzt ein: ");
        System.out.println("Die Quersumme davon ist: " + GetDigitSum(scr.nextInt()));
    }
    static int GetDigitSum(int i)
    {
        int ret = 0;
        char[] c = Integer.toString(i).toCharArray();
        for (char x: c)
        {
            ret += Character.getNumericValue(x);
        }
        return ret;
    }
}

Java-Code

class quersumme
{
    public static void checkSum() 
    {
        
        for(int i = 0; i < 100; i++) 
        {
            int summe = 0;
            String sEingabe = String.valueOf(i);
            
            for(int j = 0; j < sEingabe.length(); j++)
            {
                summe += Character.getNumericValue(sEingabe.charAt(j));
            }
            System.out.println("Quersumme von " + i + ": " + summe);
        }
    }

    public static void main (String[] args) throws java.lang.Exception
    {
        checkSum();
    }
}