/in/foo.cc: In function 'void readin()':
/in/foo.cc:8:7: warning: unused variable 's' [-Wunused-variable]
  char s[maxn];
       ^
/in/foo.cc: In function 'bool gauss(int)':
/in/foo.cc:80:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^