[c#] Carriage return and Line feed... Are both required in C#?

It's always a good idea, and while it's not always required, the Windows standard is to include both.

\n actually represents a Line Feed, or the number 10, and canonically a Line Feed means just "move down one row" on terminals and teletypes.

\r represents CR, a Carriage Return, or the number 13. On Windows, Unix, and most terminals, a CR moves the cursor to the beginning of the line. (This is not the case for 8-bit computers: most of those do advance to the next line with a CR.)

Anyway, some processes, such as the text console, might add a CR automatically when you send an LF. However, since the CR simply moves to the start of the line, there's no harm in sending the CR twice.

On the other hand, dialog boxes, text boxes, and other display elements require both CR and LF to properly start a new line.

Since there's really no downside to sending both, and both are required in some situations, the simplest policy is to use both, if you're not sure.