Help me about these codes

Yeah, sorry about the lack of information. Sorry but I don't have the codes right now, just brainstorming about what I want to do.

First, I want a command that will write a data to the serial and that command is the switch, if the switch send a logic high, the writing of data to the serial will be followed. Then another set of data will be followed.

Second, about the void reply, it is wrong, typographical error.

this is the real on:
byte RxData[8];
int i;

if(Serial.available()>0){
for(i=0; i<8; i++){
RxData = Serial.read();
Serial.print(RxData*, HEX);*
}
if(RxData[4] == 0x05){
* Serial.print("Hello User);}*
else{
Serial.print("No User profile");
}
Third, I call that data in the RxData[8], but I'm getting zero,
The problem is about the RxData*, like it doesn't store data at all.*