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.

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.

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

  
  

   
   24
39
0
  
  

  
  

   
   6
3
  
  

Greater New York 2000

We have carefully selected several similar problems for you:?? 1017? 1012? 1018? 1048? 1016

就是一个大数求和问题，我竟然。。。
第一次用整型，WA了
第二次没初始化，WA了
第三次AC:

#include<stdio.h>
#include<string.h>
int main(){
	char a[10000];
	int la,b[10000],sum,i;
	while(scanf("%s",a)&&strcmp(a,"0")!=0){
		la=strlen(a);
		sum=0;//各位数和 
		for(i=0;i<la;i++){
			b[i]=a[i]-'0';//字符转数字 
			sum+=b[i];//一个个求和 
			if(sum>=10)//超过10，最多18 
			sum=sum%10+sum/10;//两位数再加起来 
		}
		printf("%dn",sum);
		memset(a,sizeof(a));
		memset(b,sizeof(b));
	}
	return 0;
}

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