Morse code display

#include <LiquidCrystal.h>
#include <Thread.h>

const int ALPHABET_SIZE = 26;

const char alpha[ALPHABET_SIZE] = {'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'}; 
const String morse[81] = {".-", "-...", "-.-.", "-..", ".", "..-.", "--.", "....", "..", ".---", "-.-", ".-..", "--", "-.", "---", ".--.", "--.-", ".-.", "...", "-", "..-", "...-", ".--", "-..-", "-.--", "--.."};

const int TIME_UNIT = 70;
const int dot = TIME_UNIT;
const int dash = TIME_UNIT * 3;
const int symbol_space = TIME_UNIT; 
const int letter_space = TIME_UNIT * 3;
const int word_space = TIME_UNIT * 7;

const String reset = "......";

const int MAX_LENGTH = 4;

String set_text = "";
String morse_text = "";
String new_morse = "";
String display_text = "";

const int COLUMNS = 16, ROWS = 2;

bool scroll = true;

unsigned long counter = 0;
int last_value = 0;

// initialize the library by associating any needed LCD interface pin
// with the arduino pin number it is connected to
const int rs = 23, en = 22, d4 = 39, d5 = 41, d6 = 38, d7 = 40;
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);

void setup() {
  // set up the LCD's number of columns and rows:
  lcd.begin(COLUMNS, ROWS);
  lcd.clear();

  Serial.begin(9600);
  /*
  Thread myThread(scroll_until_not, "Welcome, morse code user! To begin, start pressing the button. To clear your text, enter 10 dots");
  myThread.run();
  */

  for (int i = 0; i < ALPHABET_SIZE; i ++){
    Serial.println(String(alpha[i]) + ": " + morse[i]);
  }
}

bool can_enter = false;

void loop() {
  int value = digitalRead(48);

  bool new_result = false;
  if (last_value != value){
    new_result = rel(value);
    // Serial.println(counter);
    counter = 0;
  }
  else{
    new_result = hold(value);
  }

  counter ++;

  if (new_result){
    scroll = false;
    // // Serial.println("Stopped scrolling");
    display_text = set_text;
    
    lcd.clear();
    int l = (display_text + morse_text + new_morse).length();
  
    if (l > 16){
      String new_text = "";
      for (int i = l - COLUMNS; i < display_text.length(); i ++){
        new_text += display_text[i];
      }
      display_text = new_text;
    }
    lcd.print(display_text + morse_text + new_morse);
    lcd.setCursor(0, 1);
    lcd.print("");
    lcd.setCursor(0, 0);
  }
  
  last_value = value;

  delay(1);
}

String get_letter(){
  String letter = "";
  
  for (int i = 0; i < ALPHABET_SIZE; i ++){
    if (morse_text == morse[i]){
      letter = alpha[i];
    }
  }

  return letter;
}

bool hold(int v){
  String past_morse = new_morse, past_morse_text = morse_text, past_set_text = set_text;
  if (v == 1){
    if (counter <= dot){
      new_morse = '.';
    }
    else if (counter >= dash){
      new_morse = '-';  
    }
  }
  else {
    if (counter >= letter_space){
      String l = get_letter();
   
      if (l != ""){
        set_text += l;

      }
      if (morse_text == reset){
        clear_text();
      }

      morse_text = "";
    }
  }
  return past_morse != new_morse || past_morse_text != morse_text || past_set_text != set_text;
}

bool rel(int v){
  String pm = morse_text, pt = set_text;
  if (v == 0){
    morse_text += new_morse;
    new_morse = "";
    
  }
  else {
    if (counter >= word_space){
      set_text += " ";
    }
  }
  return pm != morse_text || pt != set_text;  
}

void clear_text(){
  set_text = "";
}

/*
void scroll_until_not(String text){
  // Serial.println("entered");
  // Serial.println(text);
  while (scroll){
    // Serial.println("scrolling1");
    String temp_text = text;
    if (text.length() > 16){
      lcd.clear();
      lcd.print(text);
      delay(1000);
      for (int i = 1; i < text.length() - 15; i ++){
        // Serial.println("scrolling2");
        if (!scroll){
          break;
        }
        
        lcd.clear();
        
        temp_text = substr(text, i, text.length());
        
        lcd.print(temp_text);
        
        delay(300);
      }
    }
    else {
      // Serial.println("scrolling3");
      lcd.clear();
      lcd.print(text);
    }
    if (!scroll){
      break;
    }
    delay(1000);
  }
}

String substr(String t, int s, int l){
  String b = "";
  for (int i = s; i < s + l; i ++){
    if (i >= t.length()){
      break;
    }
    b += t[i];
  }
  return b;
}
*/