foo.c: In function 'main':
foo.c:12:2: warning: implicit declaration of function 'scanf_s'; did you mean 'scanf'? [-Wimplicit-function-declaration]
  scanf_s("%c", &a[0]);
  ^~~~~~~
  scanf
foo.c: In function 'compare':
foo.c:43:6: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
  if (i = n)
      ^
foo.c:45:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
/tmp/ccX5zVQ0.o: In function `main':
foo.c:(.text.startup+0x1f): undefined reference to `scanf_s'
foo.c:(.text.startup+0x66): undefined reference to `scanf_s'
collect2: error: ld returned 1 exit status

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