Digital Roots

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 53625    Accepted Submission(s): 16747

Problem Description

The
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 is repeated. 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 process must be repeated. Adding the
1 and the 2 yeilds 3, a single digit and also the digital root of 39.

Input

The
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.

Output

For each integer in the input, output its digital root on a separate line of the output.

Sample Input

24

39

0

Sample Output

6

3

分析：

1  10  19(10)  28(10)  ....

2  11  20        29(11)

3  12  21        30

4  13  22       .....

5  14  23

6  15  24

7  16  25

8  17  26

9  18  27

#include<stdio.h>
#include<string.h>
int main(){
    long int sum,len,i;
    char num[10000];
    while(scanf("%s",num) && num[0]!=‘0‘){
        
        len=strlen(num);
        sum=0;
        for(i=0;i<len;i++)
            sum+=num[i]-‘0‘;
        sum=sum%9;
        if(sum>0)
            printf("%d\n",sum%9);
        else
            printf("9\n");
    }
    return 0;
}