SOLVED! highByte, lowByte and serial send/receive

Projects Programming
18

Sorry, updated code is;

int buffer[10];
  if (Serial.available()) {
    int x = Serial.readBytesUntil('\r', buffer, 9);
    buffer[x] = '\0';
  }
  int y = atoi (buffer);
  Serial.println("recieved rpm  ");
  Serial.println(y);

error is now.....

no matching function for call to 'HardwareSerial::readBytesUntil(char, int [10], int)'

and what is this line doing??

buffer[x] = '\0';