/in/foo.cc: In function 'int main()':
/in/foo.cc:11:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i=0;i<b.length();i++){
               ~^~~~~~~~~~~
/in/foo.cc:23:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i=0;i<=c.length();i++) c[i]=k[c[i]-65];
               ~^~~~~~~~~~~~