C# to replace null values with the last element in array

This sounds a lot like Homework so all I'm gonna do is tell you how you should go about it, but the code is up to you to research.

First of all, you must read all the content of your file into a file stream and iterate over the stream to find the highest row length;

While iterating to get the Max length, also store each line in a string list ( List<string> ) so that you won't need to re-iterate over the stream again, instead you'll just iterate over this list;

After doing so, just iterate over the said list, test whether the current string length is lower than the Max length, and if it is, fill the array with all the characters in the string and when your iterative variable is equal to your stringLength, copy it and fill the rest of the spaces in the array with it.

The rest is up to you.

To expand on Hallagan's answer, here are several methods that might help you:

• File.ReadAllLines(path) - reads a text file into a string array
• File.WriteAllLines(path, array) - writes a string array into a text file
• string.PadRight(totalLenght, paddingChar) - pads a string from the right using a specified char.

using System.IO;

class Program
{
    static void Main()
    {
    string[] lines = File.ReadAllLines("Yourfile.txt");
        int  maxLength = 0;
    foreach (string line in lines)
    {
        if(line.Length > maxLength)
                  maxLength = line.Length
    }

       // After this, again iterate through lines array. For every String element in it, if the length of the string is less than the maxLength, then append last character (maxLength - line.Length) times. To get the last character you can use 
char last = line[line.Length - 1];
    }
}