/in/foo.c: In function 'Prime':
/in/foo.c:6:16: error: 'false' undeclared (first use in this function)
         return false;
                ^~~~~
/in/foo.c:6:16: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:13:12: error: 'true' undeclared (first use in this function)
     return true;
            ^~~~
/in/foo.c:14:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^