get max and min of date from comma text file

You can do as follows:

 int max, min;

        public void ReadTextFile()
        {
                string[] lines = File.ReadAllLines(ofd.FileName);
                List<int> list = new List<int>(); 

                for (int i = 0; i < lines.Length; i++)
                {
                  string[] words = lines[i].Split(',');
                  list.Add(int.Parse(words[1]));                  
                }

                max = list.Max();
                min = list.Min();       
  
        }      

Hope above help.