How to Convert the value in DataTable into a string array in c#

Very easy:

var stringArr = dataTable.Rows[0].ItemArray.Select(x => x.ToString()).ToArray();

Where DataRow.ItemArray property is an array of objects containing the values of the row for each columns of the data table.

Perhaps something like this, assuming that there are many of these rows inside of the datatable and that each row is row:

List<string[]> MyStringArrays = new List<string[]>();
foreach( var row in datatable.rows )//or similar
{
 MyStringArrays.Add( new string[]{row.Name,row.Address,row.Age.ToString()} );
}

You could then access one:

MyStringArrays.ElementAt(0)[1]

If you use linqpad, here is a very simple scenario of your example:

class Datatable
{
 public List<data> rows { get; set; }
 public Datatable(){
  rows = new List<data>();
 }
}

class data
{
 public string Name { get; set; }
 public string Address { get; set; }
 public int Age { get; set; }
}

void Main()
{
 var datatable = new Datatable();
 var r = new data();
 r.Name = "Jim";
 r.Address = "USA";
 r.Age = 23;
 datatable.rows.Add(r);
 List<string[]> MyStringArrays = new List<string[]>();
 foreach( var row in datatable.rows )//or similar
 {
  MyStringArrays.Add( new string[]{row.Name,row.Address,row.Age.ToString()} );
 }
 var s = MyStringArrays.ElementAt(0)[1];
 Console.Write(s);//"USA"
}

If that's all what you want to do, you don't need to convert it into an array. You can just access it as:

string myData=yourDataTable.Rows[0][1].ToString();//Gives you USA