• |核心|
• cout<<n%10+n/10%10+n/10/10;
• (个位+十位+百位)

#include<bits/stdc++.h>
using namespace std;

int n;

int main()
{
	cin>>n;
	cout<<n%10+n/10%10+n/10/10;
	
	return 0;
}