/in/foo.c: In function 'main':
/in/foo.c:8:2: warning: implicit declaration of function 'getchars' [-Wimplicit-function-declaration]
  getchars(ch);
  ^~~~~~~~
/tmp/cc6VNxR3.o: In function `main':
foo.c:(.text.startup+0xe): undefined reference to `getchars'
collect2: error: ld returned 1 exit status