/in/foo.c:3:1: error: unknown type name 'bool'
 bool isLeap(int n)
 ^~~~
/in/foo.c: In function 'isLeap':
/in/foo.c:14:10: error: 'true' undeclared (first use in this function)
   return true;
          ^~~~
/in/foo.c:14:10: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:15:9: error: 'false' undeclared (first use in this function)
  return false;
         ^~~~~
/in/foo.c:16:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^