//example values
str = "<Request Type="Query" Version="1.0"></Request>"
uintcrc = getCrc(str, strlen(str));

//code i don't understand

//create a byte array with a null terminator?
memset(strQueryBuffer, '', sizeof(str));
//print the values into the byte array
sprintf(strQueryBuffer, "%c%s%c", COMM_STX, str, COMM_ETX);

//append the uintcrc to the end of the byte array?
memcpy(strQueryBuffer + strlen(strQueryBuffer), &uintcrc, sizeof(uintcrc));

strQueryBuffer = COMM_STX + "<Request Type='Query' Version="1.0"></Request>" + COMM_ETX + Encoding.Ascii.GetString(BitConverter.GetBytes(uintcrc));

var str = "<Request Type='Query' Version="1.0"></Request>";
 byte[] Data = (new [] { COMM_STX }).Concat(Encoding.Ascii.GetBytes(str)).Concat(new [] { COMM_ETX }).Concat(BitConverter.GetBytes(uintcrc)).ToArray();

strQueryBuffer + strlen(strQueryBuffer)

&strQueryBuffer[strlen(strQueryBuffer)]