Arduino Variable size Array Declaration - c

Question

I get an error while trying to run the following code:
int SizeOfReadArray = 10;
int PacketLength = 5;
unsigned char rmessage[SizeOfReadArray];
unsigned long flag = 0;
unsigned char DataPacket[PacketLength];
int alternate = 1;
int remaining;
int Index;
void setup() {
// put your setup code here, to run once:
Serial.begin(115200);
}
void loop() {
PacketExtraction();
}
void PacketExtraction(){
// Read Serial Buffer store in array
Serial.readBytes(rmessage,SizeOfReadArray);
// onetime execution for getting exact message from serial buffer
if (flag == 0){
for (int j=0;j<SizeOfReadArray;j++){
// check for start of packets through header bytes
if (rmessage[j+0] == 65 && rmessage[j+1] == 65){
// store the Index for extracting packet from message array
Index = j;
remaining = SizeOfReadArray-Index+PacketLength;
flag = 1;
}
}
}
// actual packet extraction
/* take PacketLength of data from serial burffr and store the rest
for remaining bytes for next data packet construction */
if (alternate == 1){
for (int k=0;k<5;k++){
DataPacket[k]=rmessage[k+Index];
}
// storing remaining bytes form next execution
unsigned char previouspacket[remaining];
for (int k=0;k<remaining;k++){
previouspacket[k] = rmessage[k+Index+PacketLength];
}
alternate = 0;
}
/* now this time take the previously saved remaining bytes of packet
and merge them with the current packet data */
else{
for (int k=0;k<remaining;k++){
DataPacket[k] = previouspacket[k];
}
for (int k=0;k<(remaining+1);k++){
DataPacket[k+remaining] = rmessage[k];
}
alternate = 1;
}
}
Error Message:
Arduino: 1.6.1 (Windows 7), Board: "Arduino Mega or Mega 2560,
ATmega2560 (Mega 2560)"
sketch_apr04b.ino: In function 'void PacketExtraction()':
sketch_apr04b.ino:52:23: error: 'previouspacket' was not declared in
this scope
Error compiling.
This report would have more information with "Show verbose output
during compilation" enabled in File > Preferences.

Answer 1

previouspacket is only declared in the first branch of the if…then blocks.
You should move unsigned char previouspacket[remaining]; before the if statement