Digital Roots
http://acm.zju.edu.cn/show_problem.php?pid=1115
1 /*written by czk*/
2 #include <stdio.h>
3 #include <ctype.h>
4
5 int main() {
6 while(1) {
7 int sum = 0;
8 char c;
9 while(!isdigit(c=getchar()));
10 if(c=='0') break;
11 while(isdigit(c)) {
12 sum+= (c-'0');
13 c = getchar();
14 }
15 while(sum >= 10) {
16 int temp = sum;
17 sum = 0;
18 while(temp>0) {
19 sum += temp %10;
20 temp /= 10;
21 }
22 }
23 printf("%d\n", sum);
24 }
25 }