#include <LiquidCrystal_I2C.h>

#define I2C_ADDR    0x27
#define LCD_COLUMNS 16
#define LCD_LINES   2
#define VERT_PIN A0
#define HORZ_PIN A1
#define SEL_PIN  2
int counter = 0;
int vert, oldVert;

LiquidCrystal_I2C lcd(I2C_ADDR, LCD_COLUMNS, LCD_LINES);

void setup() {
  lcd.init();
  lcd.backlight();
  lcd.begin(16, 2);
  pinMode(VERT_PIN, INPUT);
  pinMode(HORZ_PIN, INPUT);
  pinMode(SEL_PIN, INPUT_PULLUP);
  Serial.begin(9600);

}

void loop() {
  vert = analogRead(VERT_PIN);
  if (vert == 1023 && oldVert < 600)
  {
    counter++;
  }
  if (vert == 0 && oldVert > 400)
  {
    counter--;
  }
  oldVert = vert;

  bool selPressed = digitalRead(SEL_PIN) == LOW;

  if(counter == 3)
  {
      MainMenu1();    
  }

  if(counter == 2)
  {
      MainMenu2();    
  }

  if(counter == 1)
  {
      MainMenu3();    
  }
}

void MainMenu1()
{
  lcd.setCursor(0, 0);
  lcd.print("Sub-menu 1");
  lcd.setCursor(0, 1);
  lcd.print("Sub-menu 2");
}
void MainMenu2()
{
  lcd.setCursor(0, 0);
  lcd.print("Sub-menu 2");
  lcd.setCursor(0, 1);
  lcd.print("Sub-menu 3");
}
void MainMenu3()
{
  lcd.setCursor(0, 0);
  lcd.print("Sub-menu 3");
  lcd.setCursor(0, 1);
  lcd.print("Sub-menu 4");
}