File I/O Encode & Decode with XOR

Hi, I wrote 2 programs which encodes and decodes a text file. Upon decoding, it decoded my original text but also added something extra. Here is my piece of code, could anyone kindly explain this occurance?

Encode ( It receives 2 arguments, first argument is the original text, the second argument receives a seed in order to generate a random number for XOR)

Code:

---

using System;
using System.Collections.Generic;
using System.Text;
using System.IO;

    class Task2a
    {
        static void Main(string[] args)
        {
            FileStream fileOutput, seedFile;
            int i;
            int seed;
            int inputNumber;
            char[] line = new char[1024];
            String strLine;

            try
            {
                StreamReader sr = new StreamReader(args[0]);

                inputNumber = Convert.ToInt32(args[1]);
                seed = randomNumber(inputNumber);

                fileOutput = new FileStream("cipher.txt", FileMode.OpenOrCreate, FileAccess.Write);
                seedFile = new FileStream("seed.txt", FileMode.OpenOrCreate, FileAccess.Write);

                StreamWriter input = new StreamWriter(fileOutput);
                StreamWriter keyInput = new StreamWriter(seedFile);

                strLine = sr.ReadLine();

                line = strLine.ToCharArray();

                for (i = 0; i < line.Length; i++)
                {
                    line[i] = (char)(line[i] ^ seed);
                    input.Write(line[i]);
                }

                keyInput.Write(seed.ToString());

                keyInput.Close();
                input.Close();
                sr.Close();
                seedFile.Close();
                fileOutput.Close();
            }
            catch (FileNotFoundException ex)
            {
                Console.WriteLine(ex.Message);
                Console.ReadLine();
                System.Environment.Exit(1);
            }
            catch (IndexOutOfRangeException ex)
            {
                Console.WriteLine(ex.Message + "\nNo files detected!");
                Console.ReadLine();
                System.Environment.Exit(1);
            }
            catch (IOException ex)
            {
                Console.WriteLine(ex.Message + "\nError Opening Output File");
                Console.ReadLine();
                System.Environment.Exit(1);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
                return;
            }
        }

        static int randomNumber(int seed)
        {
            Random random = new Random();
            return random.Next(seed);
        }
    }

---

Decode (It receives 2 arguments, first argument is the encoded text, the second argument is the key from the random generated number in the encode program)

Code:

---

using System;
using System.Collections.Generic;
using System.Text;
using System.IO;

    class Task2b
    {
        static void Main(string[] args)
        {
            FileStream fileOutput;
            int i;
            int key;
            char[] line = new char[1024];
            String strLine, str;

            try
            {
                StreamReader sr = new StreamReader(args[0]);
                StreamReader srKey = new StreamReader(args[1]);

                fileOutput = new FileStream("decoded.txt", FileMode.OpenOrCreate, FileAccess.Write);

                StreamWriter input = new StreamWriter(fileOutput);

                strLine = srKey.ReadLine();
                str = sr.ReadLine();

                key = Convert.ToInt32(strLine);

                line = str.ToCharArray();

                for (i = 0; i < line.Length; i++)
                {
                    line[i] = (char)(line[i] ^ key);
                    input.Write(line[i]);
                }

                input.Close();
                sr.Close();
                srKey.Close();
                fileOutput.Close();
            }
            catch (FileNotFoundException ex)
            {
                Console.WriteLine(ex.Message);
                Console.ReadLine();
                System.Environment.Exit(1);
            }
            catch (IndexOutOfRangeException ex)
            {
                Console.WriteLine(ex.Message + "\nNo files detected!");
                Console.ReadLine();
                System.Environment.Exit(1);
            }
            catch (IOException ex)
            {
                Console.WriteLine(ex.Message + "\nError Opening Output File");
                Console.ReadLine();
                System.Environment.Exit(1);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
                return;
            }
        }
    }

---

My input text

Code:

---

This is a test

---

My encoded text

Code:

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Plmw$mw$e$pawp09119361013611297119112

---

My decoded text

Code:

---

This is a test4=55=7254572556=355=556

---

There is a problem with the encoding, the encoded text should have the exact same length than the plaintext, thus there seems to be a problem with how much you write to the file.

I'm not an expert in C++ but I suppose the problem is somewhere here:

Code:

---

                for (i = 0; i < line.Length; i++)
                {
                    line[i] = (char)(line[i] ^ seed);
                    input.Write(line[i]);
                }

---

Its in C#. I'm relatively new in C#, perhaps its because of the size I've declared? What should I do to overcome this? I thought that

Code:

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line.Length

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on the for loop would just traverse until the last existing character in my char array?