ZOJ 1115 Digital Roots

Digital RootsTime Limit: 2 Seconds Memory Limit: 65536 KBBackgroundThe digital root of a positive integer is found by summing the digits of the integer. If the resulting value is a single digit then that digit is the digital root. If the resulting value contains two or more digits, those digits are summed and the process isrepeated. This is continued as long as necessary to obtain a single digit.For example, consider the positive integer 24. Adding the 2 and the 4 yields a value of 6. Since 6 is a single digit, 6 is the digital root of 24. Now consider the positive integer 39. Adding the 3 and the 9 yields 12. Since 12 is not a single digit, the processmust be repeated. Adding the 1 and the 2 yeilds 3, a single digit and also the digital root of 39.InputThe input file will contain a list of positive integers, one per line. The end of the input will be indicated by an integer value of zero.OutputFor each integer in the input, output its digital root on a separate line of the output.ExampleInput

24
39
0

Output

6
3

题意：输入一个数字，让它各个位上的数字相加，直到加到个位数为止

思路：下面那个代码是我从别人那看来的，其实就是找到个规律，不然按传统想法一直判断比较麻烦，也可能会超时间

代码：

#include<stdio.h>int main(){char dig[1024];int i,sum=0;while(scanf("%s",dig)==1&&dig[0]!='0'){for(i=0;dig[i]!='\0';i++)sum+=dig[i]-'0';printf("%d\n",sum%9==0?9:sum%9);sum=0;}return 0;}