Pass DateTime.Add function as parameter

switch (E.RepMode)
{
    case "daily":
        repeats.Add(GenerateRepeats(entry.DateStart, entry.DateEnd, 1, DateTime.AddDays));
        break;
    case "weekly":
        break;
    case "monthly":
        break;
    case "yearly":
        break;
}

public List<EntryRepeat> GenerateRepeats(DateTime start, DateTime end, int interval, Func<double, DateTime> f)
{
    do
    {

    }
    while (true);
}