uva 424 Integer Inquiry

#include<iostream>
#include<cctype>
#include<cstdlib>
#include<cstring>
using namespace std;

int main(){
    char a[110][110];
    int result[110];
    int num = 0,index;
    memset(a,'a',sizeof(a));        //没有初始化，wa 了好几次
    memset(result,0,sizeof(result));
    string s;
    while(cin >> s){
        if(s[0] == '0')
            break;
        index = 0;
        for(int i = s.length() - 1; i >= 0; i--)  //将读入的字符串反转，低位在前
            a[num][index++] = s[i];
        num++;
    }
    int c = 0;
    for(int i = 0; i < 110; i++){
        int sum = 0;
        for(int j = 0; j < num; j++){
            if(isdigit(a[j][i]))
                sum += a[j][i] - '0';
        }
        sum += c;
        c = sum / 10;
        result[i] = sum % 10;
    }
    int k;
    for(k = 109; result[k] == 0; k--);           //忽略前导0
    for(;k>=0;k--)
        cout << result[k];
    cout << endl;
    return 0;
}