c# datatable parameter

I think you need to consider splitting this

public DataTable create(string a)
{
            DataTable dt = new DataTable();
            dt.Columns.Add("Saheler",typeof(String));
            DataRow row = dt.NewRow();
            row[0] = a;
            dt.Rows.Add(row);
}

Into Something like

public DataTable create(string a)
{
            DataTable dt = new DataTable();
            dt.Columns.Add("Saheler",typeof(String));
            return dt;
}

public AddRowToDT(ref Datatable dt, String Parameter)
{
            DataRow row = dt.NewRow();
            row[0] = Parameter;
            dt.Rows.Add(row);
}

Given your description of what you're trying to do ...

If you want to elaborate further, and be a bit more specific, you might get a better answer