/in/foo.c: In function 'main':
/in/foo.c:6:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
  gets(s);
  ^~~~
In file included from /in/foo.c:1:0:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.c:8:2: error: unknown type name 'bool'
  bool flag;
  ^~~~
/in/foo.c:15:10: error: 'true' undeclared (first use in this function)
     flag=true;
          ^~~~
/in/foo.c:15:10: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:18:10: error: 'false' undeclared (first use in this function)
     flag=false;break;
          ^~~~~