uva 10929 - You can say 11

 #include <cstdio>
 using namespace std;

 char in[];

 int main()
 {
     while(gets(in))
     {
         if(in[] == '' && in[] == ) break;

         int s = ;
         for (int i = ; in[i] != ; i++)
         {
             s += (in[i] - '');
             s *= ;
             s %= ;
         }
         printf(s ==  ? "%s is a multiple of 11.\n" : "%s is not a multiple of 11.\n", in);
     }
     return ;
 }

第二种思路不错，多想想！

 #include<iostream>
 #include<string>

 using namespace std;

 int main(){
     //freopen("in.txt","r",stdin);
     //freopen("out.txt","w",stdout);

     char num[];

     int sum;

     while(){
         cin>>num;

         if(num[]=='' && strlen(num)==) break;

         sum=;

         for(int i=;i<strlen(num);i+=) sum+=num[i]-'';
         for(int i=;i<strlen(num);i+=) sum-=num[i]-'';
         cout << "sum: " << sum << endl;
         if(sum%==) cout<<num<<" is a multiple of 11."<<endl;
         else cout<<num<<" is not a multiple of 11."<<endl;
     }
 }