Open text file, loop through contents and check against

Question

So I have a generic number check that I am trying to implement:

    public static bool isNumberValid(string Number)
    {
    }

And I want to

Answer 1

You don't need to read the entire file into memory all at once. You can write:

using (var writer = new StreamWriter(outputPath))
{
    foreach (var line in File.ReadLines(filename)
    {
        foreach (var num in line.Split(','))
        {
            writer.Write(num + " ");
            writer.WriteLine(IsNumberValid(num));
        }
    }
}

The primary advantage here is a much smaller memory footprint, as it only loads a small part of the file at a time.