C# adding a character in a string

Question

I know I can append to a string but I want to be able to add a specific character after every 5 characters within the string

from this string alpha = abcdefghijklmno

Answer 1

Inserting Space in emailId field after every 8 characters

public string BreakEmailId(string emailId) {
    string returnVal = string.Empty;
    if (emailId.Length > 8) {           
        for (int i = 0; i < emailId.Length; i += 8) {
            returnVal += emailId.Substring(i, 8) + " ";
        }
    }

    return returnVal;
}