An array of List in c#

You do like this:

List<int>[] a = new List<int>[100];

Now you have an array of type List<int> containing 100 null references. You have to create lists and put in the array, for example:

a[0] = new List<int>();

Since no context was given to this question and you are a relatively new user, I want to make sure that you are aware that you can have a list of lists. It's not the same as array of list and you asked specifically for that, but nevertheless:

List<List<int>> myList = new List<List<int>>();

you can initialize them through collection initializers like so:

List<List<int>> myList = new List<List<int>>(){{1,2,3},{4,5,6},{7,8,9}};

simple approach:

        List<int>[] a = new List<int>[100];
        for (int i = 0; i < a.Length; i++)
        {
            a[i] = new List<int>();
        }

or LINQ approach

        var b = Enumerable.Range(0,100).Select((i)=>new List<int>()).ToArray();