(C#) Read Excel file content

<div>        <%-- File Upload Control  Used to upload the file to be read and obtain the file information through this control --%>
<asp:FileUpload ID="fileSelect" runat="server" />         
<%-- Click this button to execute the reading method--%>
<asp:Button ID="btnRead" runat="server" Text="ReadStart" />
</div>

//Declare variables (attributes)
string currFilePath = ; //The full path of the file to be read
string currFileExtension = ;  //File extension

//Page_Load event Register button click event
 protected void Page_Load(object sender,EventArgs e)
 {
     += new EventHandler(btnRead_Click);
 }

 
//Button click event //The 3 methods inside will be given below
 protected void btnRead_Click(object sender,EventArgs e)
 {
Upload();  //Upload file method
     if( ==".xlsx" || ==".xls")
       {
DataTable dt = ReadExcelToTable(currFilePath); //Read Excel files (.xls and .xlsx formats)
       }
       else if( == ".csv")
         {
DataTable dt = ReadExcelWidthStream(currFilePath); //Read .csv format file
         }
 }

///<summary>
///Upload the file to the temporary directory
///</ummary>
private void Upload()
{
HttpPostedFile file = ;
string fileName = ;
string tempPath = (); //Get the system temporary file path
fileName = (fileName); //Get file name (without path)
= (fileName); //Get the file extension
= tempPath + fileName; //Get the uploaded file path and record to the global variable declared earlier
(); //Upload
}

///<summary>
///How to read an Excel file in xls\xlsx format
///</ummary>
///<param name="path">The full path to Excel to be read</param>
///<returns></returns>
private DataTable ReadExcelToTable(string path)
{
//Connection string
string connstring = "Provider=.12.0;Data Source=" + path + ";Extended Properties='Excel 8.0;HDR=NO;IMEX=1';"; // Office 07 and above cannot have extra spaces, and pay attention to semicolons
//string connstring = Provider=.4.0;Data Source=" + path + ";Extended Properties='Excel 8.0;HDR=NO;IMEX=1';"; //Office 07 version below because I use Office2010, this connection string is not used. You can choose according to your own situation or the program determines which connection string to use
using(OleDbConnection conn = new OleDbConnection(connstring))
{
();
DataTable sheetsName = (,new object[]{null,null,null,"Table"}); //Get the names of all sheets
string firstSheetName = [0][2].ToString(); //Get the name of the first sheet
string sql = ("SELECT * FROM [{0}],firstSheetName); //Query string
OleDbDataAdapter ada =new OleDbDataAdapter(sql,connstring);
DataSet set = new DataSet();
(set);
return [0];

}
}

///<summary>
/// Method to read Excel file in csv format
///</ummary>
///<param name="path">The full path to Excel to be read</param>
///<returns></returns>
private DataTable ReadExcelWithStream(string path)
{
DataTable dt = new DataTable();
bool isDtHasColumn = false; //Tag whether the column has been generated by DataTable
StreamReader reader = new StreamReader(path,); //Data stream
while(!)
{
string meaage = ();
string[] splitResult = (new char[]{','},); //Read a line, separated by commas, and save into array
DataRow row = ();
for(int i = 0;i<;i++)
{
if(!isDtHasColumn) //If no column has been generated
{
("column" + i,typeof(string));
}
row[i] = splitResult[i];
}
(row); //Add row
isDtHasColumn = true; //After reading the first row, marking that the existing column is already there. When reading the subsequent rows, no column will be generated.
}
return dt;
}