/in/foo.cc: In function 'int main()':
/in/foo.cc:9:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  while(i<=s.size()){
        ~^~~~~~~~~~
/in/foo.cc:16:13: error: invalid operands of types '<unresolved overloaded function type>' and 'int' to binary 'operator<<'
     stk.push<<((s[i]-'0'*10)+s[i]-'0');
     ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~