Change date format from MM/DD/YYYY to DD/MM/YYYY

string str = null;
string[] strArr = null;

//str = strdate;
str = modifytext;
char[] splitchar = { '/' };

strArr = str.Split(splitchar);

string[] field = str.ToString().Split(("/").ToCharArray());

//string[] dateparts = new string[4];

string DDDD = field[0].ToString();

string MMMM = field[1].ToString();

string YYYY1 = field[2].ToString();

if ((field[0].ToString() == "1") || (field[0] == "2") || (field[0] == "3") || (field[0] == "4") || (field[0] == "5") || (field[0] == "6") || (field[0] == "7") || (field[0] == "8") || (field[0] == "9"))
{
DDDD = "0" + field[0].ToString();
}
else
{
DDDD = field[0].ToString();
}

if ((field[1] == "1") || (field[1] == "2") || (field[1] == "3") || (field[1] == "4") || (field[1] == "5") || (field[1] == "6") || (field[1] == "7") || (field[1] == "8") || (field[1] == "9"))
{
MMMM = "0" + field[1].ToString();
}
else
{
MMMM = field[1].ToString();
}

YYYY1 = field[2].ToString();

retdate = field[1] + "/" + field[0] + "/" + field[2];