/in/foo.c:2:1: error: unknown type name 'using'
 using namespace std;
 ^~~~~
/in/foo.c:2:17: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'std'
 using namespace std;
                 ^~~
/in/foo.c: In function 'pd':
/in/foo.c:7:20: error: 'false' undeclared (first use in this function); did you mean 'fclose'?
   if(n%i==0)return false;
                    ^~~~~
                    fclose
/in/foo.c:7:20: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:8:9: error: 'true' undeclared (first use in this function)
  return true;
         ^~~~
/in/foo.c:9:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^