StreamReader using arraylist or array

Question

Here's my code:

StreamReader reader = new StreamReader("war.txt");
string input = null;

while ((input = reader.ReadLine()) != null)
{
    Console.WriteLine(input);
}

reader.Close();

The program above reads and prints out from the file “war.txt” line-by-line. I need to re-write the program so that it prints out in reverse order, i.e., last line first and first line last. For example, if “war.txt” contains the following:

Hello.

How are you?

Thank you.

Goodbye.

The program should prints out:

Goodbye.

Thank you.

How are you?

Hello.

I am very new in C# please help! Thanks!

Answer 1

To do that, you are going to have to buffer the data anyway (unless you do some tricky work with the FileStream API to read the file backwards). How about just:

var lines = File.ReadAllLines("war.txt");
for(int i = lines.Length - 1; i >= 0; i--)
    Console.WriteLine(lines[i]);

which just loads the file (in lines) into an array, and then prints the array starting from the end.

A LINQ version of that would be:

foreach(var line in File.ReadLines("war.txt").Reverse())
    Console.WriteLine(line);

but frankly the array version is more efficient.