private void DeleteLine(int a_line)
    int start_index = richTextBox.GetFirstCharIndexFromLine(a_line);
    int count = richTextBox.Lines[a_line].Length;
    // Eat new line chars
    if (a_line < richTextBox.Lines.Length - 1)
        count += richTextBox.GetFirstCharIndexFromLine(a_line + 1) -
            ((start_index + count - 1) + 1);
    richTextBox.Text = richTextBox.Text.Remove(start_index, count);
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C# – Calculate relative time in C#

Jeff, your code is nice but could be clearer with constants (as suggested in Code Complete).
const int SECOND = 1;
const int MINUTE = 60 * SECOND;
const int HOUR = 60 * MINUTE;
const int DAY = 24 * HOUR;
const int MONTH = 30 * DAY;
var ts = new TimeSpan(DateTime.UtcNow.Ticks - yourDate.Ticks);
double delta = Math.Abs(ts.TotalSeconds);
if (delta < 1 * MINUTE)
  return ts.Seconds == 1 ? "one second ago" : ts.Seconds + " seconds ago";
if (delta < 2 * MINUTE)
  return "a minute ago";
if (delta < 45 * MINUTE)
  return ts.Minutes + " minutes ago";
if (delta < 90 * MINUTE)
  return "an hour ago";
if (delta < 24 * HOUR)
  return ts.Hours + " hours ago";
if (delta < 48 * HOUR)
  return "yesterday";
if (delta < 30 * DAY)
  return ts.Days + " days ago";
if (delta < 12 * MONTH)
  int months = Convert.ToInt32(Math.Floor((double)ts.Days / 30));
  return months <= 1 ? "one month ago" : months + " months ago";
  int years = Convert.ToInt32(Math.Floor((double)ts.Days / 365));
  return years <= 1 ? "one year ago" : years + " years ago";
    
C# – How to cast int to enum

From an int:
YourEnum foo = (YourEnum)yourInt;
From a string:
YourEnum foo = (YourEnum) Enum.Parse(typeof(YourEnum), yourString);
// The foo.ToString().Contains(",") check is necessary for enumerations marked with an [Flags] attribute
if (!Enum.IsDefined(typeof(YourEnum), foo) && !foo.ToString().Contains(","))
    throw new InvalidOperationException($"{yourString} is not an underlying value of the YourEnum enumeration.")
Update:
From number you can also
YourEnum foo = (YourEnum)Enum.ToObject(typeof(YourEnum) , yourInt);
            
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