C#

public enum TcpHeaderFlags : byte
{
    CWR = 128,
    ECE = 64,
    URG = 32,
    ACK = 16,
    PSH = 8,
    RST = 4,
    SYN = 2,
    FIN = 1,
    None = 0
}

public class TcpHeader : ProtocolHeader
{

    //Fields
    public UInt16 SourcePort = 80;
    public UInt16 DestinationPort = 80;
    public UInt32 SequenceNumber = 0;
    public UInt32 AcknowledgmentNumber = 0;
    private byte DataOffsetAndReserved = 0;
    public TcpHeaderFlags Flags = TcpHeaderFlags.None;
    public UInt16 WindowSize = UInt16.MaxValue;
    public UInt16 Checksum = 0;
    public UInt16 UrgentPointer = 0;

    public override byte[] GetProtocolPacketBytes(byte[] payLoad)
    {
        //Stream
        MemoryStream memStream = new MemoryStream();

        //Buffer
        byte[] buffer = null;

        //Source port
        buffer = BitConverter.GetBytes(SourcePort);
        memStream.Write(buffer, 0, buffer.Length);

        //Destination port
        buffer = BitConverter.GetBytes(DestinationPort);
        memStream.Write(buffer, 0, buffer.Length);

        //Sequence number
        buffer = BitConverter.GetBytes(SequenceNumber);
        memStream.Write(buffer, 0, buffer.Length);

        //Ack number
        buffer = BitConverter.GetBytes(AcknowledgmentNumber);
        memStream.Write(buffer, 0, buffer.Length);

        //Data offset and reserved
        memStream.Write(new byte[] { DataOffsetAndReserved }, 0, 1);

        //Flags
        memStream.Write(new byte[] { (byte)Flags }, 0, 1);

        //Window size
        buffer = BitConverter.GetBytes(WindowSize);
        memStream.Write(buffer, 0, buffer.Length);

        //Checksum
        buffer = BitConverter.GetBytes(Checksum);
        memStream.Write(buffer, 0, buffer.Length);

        //Urgent pointer
        buffer = BitConverter.GetBytes(UrgentPointer);
        memStream.Write(buffer, 0, buffer.Length);

        //Return
        return memStream.ToArray().Concat(payLoad).ToArray();
    }

}