Hello, so sorry to bother you. Would you mind quickly helping me out with a problem I have concerning my question on StackExchange (arduino.stackexchange.com/…)?

#include <SoftwareSerial.h>
SoftwareSerial BTserial(2, 3); // RX, TX

void setup() {
Serial.begin(9600);
BTserial.begin(9600);
Serial.println("Communication with HC-05 successfully started.");
}

const char* BOOK_UPLOAD_START_TAG = "(__BOOK_UPLOAD_START__)";
const char* BOOK_UPLOAD_END_TAG = "(__BOOK_UPLOAD_END__)";
int tag_pos = 0;
char c;
bool is_uploading_book = false;

#define DELAY_SIZE 50
char delay_chars[DELAY_SIZE];
int update_count = 0;

void loop(){
if (BTserial.available()) {
c = BTserial.read();
if (is_uploading_book) {
Serial.write(c);
if(update_count < DELAY_SIZE) {
delay_chars[update_count] = c;
} else {
for (int i = 0; i < (DELAY_SIZE - 1); i++) {
delay_chars[i] = delay_chars[i + 1];
delay_chars[DELAY_SIZE - 1] = c;
}

// Checking if the end tag is in the delay_chars
for (int i = 0; i < (DELAY_SIZE - 1); i++) {
if (check_tag_in_char(delay_chars[i], BOOK_UPLOAD_END_TAG)) {
tag_pos = 0;
Serial.println("Uploaded");
is_uploading_book = false;
}
}
}
update_count++;
} else {
if (check_tag_in_char(c, BOOK_UPLOAD_START_TAG)) {
tag_pos = 0;
Serial.println("Starting");
is_uploading_book = true;
}
}
}

}

int check_tag_in_char(char a, const char* TAG_STR) {
if (a == TAG_STR[tag_pos]) { tag_pos++; } else if (a == TAG_STR[0]) { tag_pos = 1; } else { tag_pos = 0; }
if (TAG_STR[tag_pos] == '\0') {
return true;
} else {
return false;
}
}