C# csharp read from file write into file

public static string ReadFile(string f){
            System.IO.StreamReader file = new System.IO.StreamReader(f);
            string testxmldata = file.ReadToEnd(); file.Close();
            return testxmldata;
        }
public  void WriteIntoFile(string path,string m) {
                if (!File.Exists(path)) {
                    // Create a file to write to.
                    using (StreamWriter sw = File.CreateText(path)) {
                        sw.WriteLine(m);
                    }
                }
                else {
                    // This text is always added, making the file longer over time
                    // if it is not deleted.
                    using (StreamWriter sw = File.AppendText(path)) {
                        sw.WriteLine(m);
                    }
                }
}

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