How do I add a UDP header to this....

typedef struct _IP_HEADER_
{
   BYTE  ver_ihl;        // Version (4 bits) and Internet Header Length (4 bits)
   BYTE  type;           // Type of Service (8 bits)
   WORD  length;         // Total size of packet (header + data)(16 bits)
   WORD  packet_id;      // (16 bits)
   WORD  flags_foff;     // Flags (3 bits) and Fragment Offset (13 bits)
   BYTE  time_to_live;   // (8 bits)
   BYTE  protocol;       // (8 bits)
   WORD  hdr_chksum;     // Header check sum (16 bits)
   DWORD source_ip;      // Source Address (32 bits)
   DWORD destination_ip; // Destination Address (32 bits)
} IPHEADER;

typedef struct _TCP_HEADER_
{
   WORD  source_port;       // (16 bits)
   WORD  destination_port;  // (16 bits)
   DWORD seq_number;        // Sequence Number (32 bits)
   DWORD ack_number;        // Acknowledgment Number (32 bits)
   WORD  info_ctrl;         // Data Offset (4 bits), Reserved (6 bits), Control bits (6 bits)
   WORD  window;            // (16 bits)
   WORD  checksum;          // (16 bits)
   WORD  urgent_pointer;    // (16 bits)
} TCPHEADER;

typedef struct _ICMP_HEADER_
{
   BYTE type;               // (8 bits)  
   BYTE code;               // (8 bits)  
   WORD checksum;           // (16 bits)  
} ICMPHEADER;