/in/foo.c: In function 'main':
/in/foo.c:13:2: warning: implicit declaration of function 'ptintf' [-Wimplicit-function-declaration]
  ptintf("\n");
  ^~~~~~
/tmp/ccnwZDpq.o: In function `main':
foo.c:(.text.startup+0xaa): undefined reference to `ptintf'
collect2: error: ld returned 1 exit status