/in/foo.cc: In function 'int main()':
/in/foo.cc:10:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(i=0;i<=s.length()-n;i++)
          ~^~~~~~~~~~~~~~
/in/foo.cc:13:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   while(j<s.length() && cnt<n)
         ~^~~~~~~~~~~
/in/foo.cc:21:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   while(j<s.length() && a[s[j++]-'a']!=0)
         ~^~~~~~~~~~~
/in/foo.cc:23:23: error: 'memset' was not declared in this scope
   memset(a,0,sizeof(a));
                       ^