HDU 1013 Digital Roots

#include<stdio.h>
#include<string.h>

int main() {
char s[10001];
memset(s, '0', sizeof(s));
while(~scanf("%s", s)){
if(s[0] == '0') break;
int ssum;
while(1) {
int sum = 0;
for(int i = 0; i < strlen(s); i++)
sum += (s[i] - '0');
ssum = sum;
// printf("HQL %d\n", sum);
if(sum < 10) break;
sprintf (s, "%d", sum);
// printf("HQL %s\n", s);
}
memset(s, '0', sizeof(s));
printf("%d\n", ssum);
}
return 0;
}