Issues to write and read TXT files in C#

/// <summary>
/// Write strings to txt file/// </summary>
/// <param name="value">Content</param>/// <param name="isClearOldText">Whether to clear old text</param>private void Wriete(string value, bool isClearOldText = true)
{
    string path = "Path to txt file";
    //Whether to clear the old text    if (isClearOldText)
    {
        //Clear the txt file        using (FileStream stream = (path, , ))
        {
            (0, );
            (0);
        }
    }
    //Write content    using (StreamWriter writer = new StreamWriter(path, true))
    {
        (value);
    }
}

/// <summary>
/// Read the txt file and return the contents in the file/// </summary>
/// <returns>txt file content</returns>private string ReadTxTContent()
{
    try
    {
        string s_con = ;
        // Create an instance of StreamReader to read the file        // Using statement can also close StreamReader        using (StreamReader sr = new StreamReader("Path to txt file"))
        {
            string line;
            // Read and display lines from the file until the end of the file            while ((line = ()) != null)
            {
                s_con += line;
            }
        }
        return s_con;
    }
    catch (Exception e)
    {
        ();
        return null;
    }
} 

//Format statement<!--?xml version="1.0" -->
useencodingCoding of attribute declaration document     
<!--?xml version="1.0" encoding="UTF-8" -->
usestandaloneAttribute description whether the document is independent     
<!--?xml version="1.0" encoding="UTF-8" standalone="yes" --> 

<?xml version="1.0" encoding="utf-8"?> 
<xcsharp > 
  <app > 
    <name>Advanced Mathematics</name>
    <age>12</age>
  </app>
</xcsharp >

static void Main(string[] args)
{
     //Load the XML file in     XDocument document = ("E:\\");
     //Get the root element of the XML to operate     XElement root= ;
     XElement ele= ("app");
     //Get the value of the name tag     XElement shuxing= ("app");
     ();
     //Get all child elements under the root element     IEnumerableenumerable = ();
     foreach (XElement item in enumerable)
     {
         foreach (XElement item1 in ())
         {
             ();         
         }
         (("id").Value); 
     }   
     ();
}

static void Main(string[] args)
{
     //Get the root node object     XDocument document = new XDocument();
     XElement root = new XElement("xcsharp");
     XElement book = new XElement("app");
     ("name", "test");
     ("age", "12");
     (app);
     ("e:\\");      
     ();
}