How to insert a space into a string, between every 4 characters? [duplicate]

Question

The string displays value as:

123456789012

I need it like:

1234 5678 9012

There should be space between every 4 characters in this string. How do I do that?

displaynum_lbl.Text = Regex.Replace(printClass.mynumber.ToString(), ".{4}", "$0");

Answer 1

        String abc = "123456789012";

        for (int i = 4; i <= abc.Length; i += 4)
        {
            abc = abc.Insert(i, " ");
            i++;
        }

Answer 2

Assuming that it's fine to work from right-to-left, this should do the trick:

displaynum_lbl.Text = System.Text.RegularExpressions.Regex.Replace(printClass.mynumber.ToString(), ".{4}", "$0 ");

You can find that and a good deal more information in other StackOverflow answers, example: Add separator to string at every N characters?