preserving Array elements using c#.net

Consider the two arrays:
        string[] str = new string[1];
            str[0] = "str";
            string[] str1 = new string[2];
            str1[0] = "str1";
            str1[1] = "str2";

To append an two arraycollections:
str = str.Concat(str1).ToArray(); //the  result was stored in the str array. this will work only in .net 2008

To add new element in the array:
        Array.Resize(ref str, newSize);
            str[newSize-1] = "newvalue";