Replace use of '%as' (and '%a[...]') scanf directives with '%ms'
POSIX.1-2008 specifies '%ms' - the use of '%as' (etc.) is discouraged because it conflicts with ISO C. With glibc ≥ 2.29, this specifier is not available unless the program is compiled in C89 mode.
It should be no problem to use the more modern '%m', so let's do that.