return Enumerable.Range(-7, 7).Select(x => d.AddDays(x).ToString()).ToArray();

------解决方案--------------------
DateTime dt = new DateTime(year, month, day);
dt.AddDays(-1);    //周四
Console.WriteLine(dt.ToString("dd-MM-yy"));

------解决方案--------------------
C# code

        private string[] Get7days(DateTime d)
        {
            string[] str = new string[7];
            for (int i = 0; i < 7; i++)
            {
                DateTime dt = d.AddDays(-1 * i);
                str[6 - i] = dt.DayOfWeek.ToString();
            }
            return str;
        }