/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 'void solve(int)':
/in/foo.cc:88:34: warning: the omitted middle operand in ?: will always be 'true', suggest explicit middle operand [-Wparentheses]
    printf("%d%c",B[i*m+j],j==m-1?:'\n':' ');
                                  ^
/in/foo.cc:88:39: error: expected ')' before ':' token
    printf("%d%c",B[i*m+j],j==m-1?:'\n':' ');
                                       ^
/in/foo.cc: In function 'bool gauss(int)':
/in/foo.cc:80:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^