M - 枚舉答案能不能做？

題目描述

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

思路：

題意：將一個數的每一位加起來，如果和爲個位數，輸出；否則，重複該過程；
思路：
這個“數”可能非常大，遠遠超出已有的數據類型的範圍，所以不能定義一個數據類型來存儲輸入的數;(一開始一直wa)
改用讀取一位，處理一位的方法；
使用“合九法”；

代碼

#include <stdio.h>
#include <string.h>
using namespace std;
int main()
{
    char a;
    int sum=0;
    while(a=getchar()){//輸入
        if(a=='\n'){//一行輸入結束
            if(sum!=0){
                printf("%d\n",sum%9?sum%9:9);
                sum=0;
            }
            else
                break;
        }
        else if(a>='0'&&a<='9'){
            sum+=a-'0';
            //sum=sum%9;
        }
    }
    return 0;
}

M - 枚舉答案能不能做？