Split and Merge files in C#

private void btnSplit_Click(object sender, EventArgs e)
{
    string inputFile = txtInputFile.Text; // Substitute this with your Input File 
    FileStream fs = new FileStream(inputFile, FileMode.Open, FileAccess.Read);
    int numberOfFiles = Convert.ToInt32(txtChunks.Text);
    int sizeOfEachFile = (int)Math.Ceiling((double)fs.Length / numberOfFiles);

    for (int i = 1; i <= numberOfFiles; i++)
    {
        string baseFileName = Path.GetFileNameWithoutExtension(inputFile);
        string extension = Path.GetExtension(inputFile);
        FileStream outputFile = new FileStream(Path.GetDirectoryName(inputFile) + "\\" + baseFileName + "." + i.ToString().PadLeft(5, Convert.ToChar("0")) + extension + ".tmp", FileMode.Create, FileAccess.Write);
        int bytesRead = 0;
        byte[] buffer = new byte[sizeOfEachFile];

        if ((bytesRead = fs.Read(buffer, 0, sizeOfEachFile)) > 0)
        {
            outputFile.Write(buffer, 0, bytesRead);
        }
        outputFile.Close();
    }
    fs.Close();
}

private void btnMerge_Click(object sender, EventArgs e)
{
    string outPath = txtInputFolder.Text; // Substitute this with your Input Folder 
    string[] tmpFiles = Directory.GetFiles(outPath, "*.tmp");
    FileStream outputFile = null;
    string prevFileName = "";

    foreach (string tempFile in tmpFiles)
    {

        string fileName = Path.GetFileNameWithoutExtension(tempFile);
        string baseFileName = fileName.Substring(0, fileName.IndexOf(Convert.ToChar(".")));
        string extension = Path.GetExtension(fileName);

        if (!prevFileName.Equals(baseFileName))
        {
            if (outputFile != null)
            {
                outputFile.Flush();
                outputFile.Close();
            }
            outputFile = new FileStream(outPath + baseFileName + extension, FileMode.OpenOrCreate, FileAccess.Write);
        }
        
        int bytesRead = 0;
        byte[] buffer = new byte[1024];
        FileStream inputTempFile = new FileStream(tempFile, FileMode.OpenOrCreate, FileAccess.Read);

        while ((bytesRead = inputTempFile.Read(buffer, 0, 1024)) > 0)
            outputFile.Write(buffer, 0, bytesRead);

        inputTempFile.Close();
        File.Delete(tempFile);
        prevFileName = baseFileName;
    }
    outputFile.Close();
}

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