/in/foo.cc: In function 'int read()':
/in/foo.cc:8:43: error: unable to find numeric literal operator 'operator""ch'
  while((ch<='0')&&(ch>'9')) s*=ch=='-'?-1:1ch=getchar();
                                           ^~~
/in/foo.cc:8:43: note: use -std=gnu++11 or -fext-numeric-literals to enable more built-in suffixes