Valid ID

1. Suppose we want to test whether an input string matches the following rules:
   1. String length is 10.
   2. The first character is an uppercase letter.
   3. The second character is either '1' or '2'.
   4. The remaining 8 digits can be among '0' ~ '9'.
2. Write a function to test a string.

   int main()
   {
       string s;
       while (cin >> s)
       {
           if (valid_id(s))
               cout << s << " is valid.\n";
           else
               cout << s << " is NOT valid.\n";
       }
       return 0;
   }  

3. You may test your program with these data.