今天來解YKL27(UVA11332)：Summing Digits

Summing Digits

跟題目敘述的一樣
f(n) = 1+2+3+4+5+6+7+8+9+2 = 47
f(f(n)) = 4 + 7 = 11
f(f(f(n))) = 1 + 1 = 2

用下方
sum += num%10;
num/=10;

#include <iostream>
#include <string>

using namespace std;

int plusdig(int num){
	while(num >= 10){
		int sum=0;
		while(num > 0){
			sum += num%10;
			num/=10;
		}
		num = sum;
	}
	return num;
}
int main(){
	int num;
	while(cin >> num){
		if(num==0)break;
		cout << plusdig(num) << endl;
	}
	return 0;
}