/in/foo.c: In function 'input':
/in/foo.c:5:3: warning: implicit declaration of function 'scanf_s' [-Wimplicit-function-declaration]
   scanf_s("%d", &a[i]);
   ^~~~~~~
/in/foo.c: In function 'main':
/in/foo.c:21:8: warning: unused variable 'count' [-Wunused-variable]
  int n,count=0;
        ^~~~~
/tmp/ccH1FRoW.o: In function `input':
foo.c:(.text+0x2d): undefined reference to `scanf_s'
/tmp/ccH1FRoW.o: In function `main':
foo.c:(.text.startup+0x21): undefined reference to `scanf_s'
foo.c:(.text.startup+0x4d): undefined reference to `scanf_s'
collect2: error: ld returned 1 exit status