Convert comma separated string of ints to int array

You should use a foreach loop, like this:

public static IEnumerable<int> StringToIntList(string str) {
    if (String.IsNullOrEmpty(str))
        yield break;

    foreach(var s in str.Split(',')) {
        int num;
        if (int.TryParse(s, out num))
            yield return num;
    }
}

Note that like your original post, this will ignore numbers that couldn't be parsed.

If you want to throw an exception if a number couldn't be parsed, you can do it much more simply using LINQ:

return (str ?? "").Split(',').Select<string, int>(int.Parse);

If you don't want to have the current error handling behaviour, it's really easy:

return text.Split(',').Select(x => int.Parse(x));

Otherwise, I'd use an extra helper method (as seen this morning!):

public static int? TryParseInt32(string text)
{
    int value;
    return int.TryParse(text, out value) ? value : (int?) null;
}

and:

return text.Split(',').Select<string, int?>(TryParseInt32)
                      .Where(x => x.HasValue)
                      .Select(x => x.Value);

or if you don't want to use the method group conversion:

return text.Split(',').Select(t => t.TryParseInt32(t)
                      .Where(x => x.HasValue)
                      .Select(x => x.Value);

or in query expression form:

return from t in text.Split(',')
       select TryParseInt32(t) into x
       where x.HasValue
       select x.Value;