hdu-1013 Digital Roots

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

24390

 

Sample Output

63

 

Source

Greater New York 2000 

 

题意：将输入数各位数相加，如果结构大于等于10，重复各位数相加步骤。

如24，2+4=6小于10输出， 39 3+9=12，大于等于10，重复相加步骤1+2=3。

此题陷阱在于输入的数可以为一个无限大的数，所以排除了用int和longlong装数据的想法。

对于大于longlong范围的无限大的数，只能用字符串来存放了。

#include <stdio.h>#include <string.h>char a[10010];int main(){    int n,digit,sum = 0,i;    while (scanf("%s",a)!=EOF) {        if(strcmp(a, "0")==0)            return 0;        sum=0;        for(i=0;i<strlen(a);i++)            sum=sum+a[i]-'0';        while(sum>=10){            n=sum;            sum=0;        do{            digit=n%10;            sum=sum+digit;            n=n/10;        }while(n!=0);            n=sum;        }        printf("%d\n",sum);    }}

AC代码