Content filter on C# (wwwcensor)

I use this code from examples (wwwcensor).
I try to convert it in C# language in VS.NET.
yet it does not work( please help me!!!

source C++ code:

DWORD dwDataLength = PacketBuffer.m_Length - (sizeof(ether_header) + pIpHeader->ip_hl*4 + pTcpHeader->th_off*4);

PCHAR pData = (PCHAR)pEthHeader + (sizeof(ether_header) + pIpHeader->ip_hl*4  + pTcpHeader->th_off*4);

// If packet contains any data - process it

if (dwDataLength)

{

memcpy (szTempString, pData, dwDataLength);

for (unsigned t = 0; t < dwDataLength; ++t)

{

if (szTempString[t] == 0)

szTempString[t] = 0x20;

if (isalpha((UCHAR)szTempString[t]))

szTempString[t] = (char)toupper((UCHAR)szTempString[t]);

}

szTempString[dwDataLength] = 0;

}

it’s my C# variant:

int size_ip = pIpHeader->IPLenVer * 4;

int size_tcp = pTcpHeader->Off * 4;

long dwDataLength = PacketBuffer.m_Length - sizeof(ETHER_HEADER) + size_ip + size_tcp;

char* pData = (char*)pEthHeader + sizeof(ETHER_HEADER) + size_ip + size_tcp;

string szTempString="";

if (dwDataLength>0)

{

for (int i = 0; i < dwDataLength; i++)

{

if (pData == 0)

szTempString += 0x20;

if (IsAlpha((byte)pData))

szTempString += Convert.ToChar((byte)pData);

}

szTempString += 0x00;

}

my english bad. can answer me on Russian language.