C++ :

#include<bits/stdc++.h>
using namespace std;
int main()
{
	int g,s,b,x;
	cin>>x;
	g=x%10;
	s=x/10%10;
	b=x/100;
	cout<<g+s+b;
    return 0;
}

Java :

import java.util.Scanner;
public class Main
{   
	public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int x = sc.nextInt();
        int a = x/100;
        int b = x/10%10;
        int c = x%10;
        System.out.println(a+b+c); 
    }
}