how to write a text line in a text file

[sowmyask]

I have a file named abc.txt. I want to insert the text line at line number 10 such that the content of line number 10 must be in line 11 and so on.
How do I, do this opeartion ?

[Ramy Mahrous]

Treat with array of strings, and insert into this array and when you need to reflect this changes use foreach (string s in urArrayOfStrings) { Write in your txt file}