java:

import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int sum = 0;
		while(n != 0) {
			sum += n % 10;
			n = n / 10;
		}
		System.out.println(sum);
	}
}

c++:

#include<iostream>
using namespace std;

int main()
{
	int n;
	cin>>n;
	int s,sum=0;
	while(n!=0)
	{
		s=n%10;
		n=n/10;
		sum=sum+s;
	}
	
	cout<<sum<<endl;
}