/in/foo.cc: In function 'int main()':
/in/foo.cc:11:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i = 0; i < In.size(); i++)
                 ~~^~~~~~~~~~~
/in/foo.cc:15:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if(i == In.size() - 1 && In[i] = 'X')
       ~~^~~~~~~~~~~~~~~~
/in/foo.cc:15:37: error: lvalue required as left operand of assignment
    if(i == In.size() - 1 && In[i] = 'X')
                                     ^~~