/in/foo.c:6:5: error: variably modified 'a' at file scope
 int a[maxn], n, l, sum,vis[maxn], sequence[maxn];
     ^
/in/foo.c:6:24: error: variably modified 'vis' at file scope
 int a[maxn], n, l, sum,vis[maxn], sequence[maxn];
                        ^~~
/in/foo.c:6:35: error: variably modified 'sequence' at file scope
 int a[maxn], n, l, sum,vis[maxn], sequence[maxn];
                                   ^~~~~~~~