You have not provided a length indicator. From MSDN:
Unlike scanf and wscanf, scanf_s and wscanf_s require the buffer size
to be specified for all input parameters of type c, C, s, S, or string
control sets that are enclosed in []. The buffer size in characters is
passed as an additional parameter immediately following the pointer to
the buffer or variable. For example, if you are reading a string, the
buffer size for that string is passed as follows: char s[10];
scanf_s("%9s", s, _countof(s)); // buffer size is 10, width
specification is 9
Here is a link to that page.
