Split a String by an indexes array

Disclaimer: I'm not actually very familiar with C#. I'll also refrain from the style review and let someone more familiar with common practices take a crack.

You can prepend 0 and append line.Length to your array, simplifying the logic. There's probably a better way, but I got it working with a List:

List<int> list = new List<int>();
list.Add(0);
list.AddRange(markers);
list.Add(line.Length);

for (int i = 0; i < list.Count - 1; i++)
{
    string value = line.Substring(list[i], list[i + 1] - list[i]);
    Console.WriteLine(value);
}

I would write an extension method:

public static class StringExtensions
{
    public static IEnumerable<string> SplitByIndex(this string @string, params int[] indexes)
    {
        var previousIndex = 0;
        foreach (var index in indexes.OrderBy(i => i))
        {
            if (index > @string.Length)
            {
                break;
            }
            yield return @string.Substring(previousIndex, index - previousIndex);
            previousIndex = index;
        }

        yield return @string.Substring(previousIndex);
    }
}

And use it like this:

foreach (var part in "001ABCD2T".SplitByIndex(3, 7, 8))
{
    Console.WriteLine(part);
}

--EDIT--

Explanation. It's better to encapsulate this splitting algorithm in a method so we can re-use the same code later from another place. I like to use extension methods for general-puspose methods like this. I usually implement such functionality in some common assembly in a separate namespace (for example, MyCoolProject.Extensions.String). This way anyone who needs these extension methods can simply use the corresponding namespace in his code, and others will not be troubled by unnecessary methods.

As for the algorithm itself, it does not change our index array and it yields only one substring at a time. Plus, it's a bit more readable in my opinion because we do not use indexes to access index array, we're just iterating through it.

Few helping variables and conditional operator:

string line = "001ABCD2T";
int[] markers = new int[] {3, 7, 8};

for (int i = -1, m = markers.Legth-1; i < markers.Length; i++)
{
    int from = i < 0 ? 0 : markers[i];
    int to = i == m ? line.Length : markers[i + 1];
    string value = line.Substring(from, to-from);

    Console.WriteLine(value);
}

You could do this without rebuilding the index array or any conditionals. Simply handle the first substring and the last substring outside of the loop:

string line = "001ABCD2T";
int[] markers = new int[] { 3, 7, 8 };
List<string> output = new List<string>{line.Substring(0, markers[0])};;
int i = 0;
int limit = markers.Length - 1;
for (; i < limit; i++)
{
    output.Add(line.Substring(markers[i], markers[i + 1] - markers[i]));
}
output.Add(line.Substring(markers[i], line.Length - markers[i]));

Assuming a forbidden token (cannot exist in the input string) is alright, here's a goofy idea idea using String.Split().

string line = "001ABCD2T";
int[] markers = { 3, 7, 8 };

const string tokenToSplitBy = "~";
int insertionCount = 0;

foreach (int index in markers)
    line = line.Insert(index + insertionCount++, tokenToSplitBy);

string[] resultArray = line.Split(new[]{tokenToSplitBy}, StringSplitOptions.RemoveEmptyEntries);

foreach (string result in resultArray)
    Console.WriteLine(result);