Compiling error at ATmega2560

The main issue with your code is the formatting. It seems that you have managed to 'comment out' some of the necessary { or } for some of the functions and/or if/else blocks, hence the failure to compile.

e.g.

BT.begin(9600); //set data rate in bits per second (baud) for data transmission }

The } at the end of that particular line is the closing brace for the void setup() function... but because it's after the // for the comment, the compiler won't see it, so it is effectively missing.

This code should now compile on your system... once all the missing { and } were un-commented.

#include <Wire.h>
#include <LCD.h>
#include <LiquidCrystal_I2C.h>
#include <SoftwareSerial.h>

LiquidCrystal_I2C lcd(0x27, 2, 1, 0, 4, 5, 6, 7);
SoftwareSerial BT(10, 11); //Tx and Rx pins for BT communication const int temp_sensor = 0; //pin A0 (temperature sensor) const int fan = 22; //pin D2 (fan) float temp; //temperature value

int threshold = 21; //temperature threshold

const int LDRsensor = 1; //pin A1 (lighting sensor)
const int LED1 = 6; //pin D6 (LED 1)
const int LED2 = 7; //pin D7 (LED 2)
const int LED3 = 8; //pin D8 (LED 3)
const int LED4 = 9; //pin D9 (LED 4)
const int WL_sensor = 15; //pin A15 (water level sensor)
const int Wpump = 13; //pin D13 (water pump)
const int mov_sensor = 3; //pin D3 (movement sensor)
const int LEDalrm = 4; //pin D4 (alarm LED)
const int buzzer = 5; //pin D5 (buzzer)

int LDRvalue; //natural light value
float water_level; //water level value
int mov_value; //movement value (true or false)

char state; //data sent from App
char mode;   //mode selected according to "state" value char order; //order to actuators according to "state" value

void setup() //this function is only executed one time
{
    lcd.begin(16, 2);
    lcd.setBacklightPin(3, POSITIVE);
    lcd.setBacklight(HIGH);

    lcd.setCursor(0, 0);
    lcd.print("TFG");
    lcd.setCursor(0, 1);
    lcd.print("Anna Merino");

    delay(4000);

    lcd.clear();

    pinMode(temp_sensor, INPUT); //temperature sensor Mode
    pinMode(fan, OUTPUT); //fan Mode
    pinMode(LDRsensor, INPUT); //lighting sensor Mode
    pinMode(LED1, OUTPUT); //LED1 Mode
    pinMode(LED2, OUTPUT); //LED2 Mode
    pinMode(LED3, OUTPUT); //LED3 Mode
    pinMode(LED4, OUTPUT); //LED4 Mode
    pinMode(WL_sensor, INPUT); //water level sensor Mode
    pinMode(Wpump, OUTPUT); //water pump Mode
    pinMode(mov_sensor, INPUT); //movement sensor Mode
    pinMode(LEDalrm, OUTPUT); //alarm LED Mode
    pinMode(buzzer, OUTPUT); //buzzer Mode

    BT.begin(9600); //set data rate in bits per second (baud) for data transmission
}

void loop() //function loop – continuously executed
{
    if (BT.available() > 0)
    {
        state = BT.read(); //transfer data sent by App to a local variable
    }

    if (state == 'Y')
    {
        mode = 'A';
    }
    else if (state == 'Z')
    {
        mode = 'R';
    }
    else if (state == 'X')
    {
        mode = 'D';
    }

    if (mode == 'A')
    {
        automaticmode(); //execute automatic function
    }
    else if (mode == 'R')
    {
        remotemode(); //execute remote function
    }
    else if (mode == 'D')
    {
        alarmmode(); //execute alarm function
    }
}

void alarmmode() // alarm function
{
    water_level = analogRead(WL_sensor); //data of water level sensor transmission to a local variable

    if (digitalRead(mov_sensor)) //evaluate movement captured
    {
        digitalWrite(LEDalrm, HIGH);
        digitalWrite(buzzer, HIGH);
    }
    else
    {
        digitalWrite(LEDalrm, LOW);
        digitalWrite(buzzer, LOW);
    }
    if (water_level > 100) //water level control
    {
        digitalWrite(Wpump, HIGH);
    }
    else
    {
        digitalWrite(Wpump, LOW);
    }
}

void automaticmode() // automatic function
{
    LDRvalue = analogRead(LDRsensor); //data of natural light transmission to a local variable water_level = analogRead(WL_sensor); //data of water level sensor transmission to a local variable
    temp = analogRead(temp_sensor); //data of temperature sensor transmission to a local variable temp = temp*0.4883; //adjustment of temperature value digitalWrite(LEDalrm, LOW);

    digitalWrite(buzzer, LOW);

    lcd.setCursor(0, 0);
    lcd.print("Temperature");

    lcd.setCursor(0, 1);
    lcd.print(temp); //LCD display – shows temperature value

    lcd.setCursor(7, 1);
    lcd.print("ºC");

    if (water_level > 100) //water level control
    {
        digitalWrite(Wpump, HIGH);
    }
    else
    {
        digitalWrite(Wpump, LOW);
    }

    if ((LDRvalue < 1023) & (LDRvalue >= 822)) //light control
    {
        digitalWrite(LED1, LOW);
        digitalWrite(LED2, LOW);
        digitalWrite(LED3, LOW);
        digitalWrite(LED4, LOW);
    }
    else if ((LDRvalue < 821) & (LDRvalue >= 617))
    {
        digitalWrite(LED1, HIGH);
        digitalWrite(LED2, LOW);
        digitalWrite(LED3, LOW);
        digitalWrite(LED4, LOW);
    }
    else if ((LDRvalue < 616) & (LDRvalue >= 412))
    {
        digitalWrite(LED1, HIGH);
        digitalWrite(LED2, HIGH);
        digitalWrite(LED3, LOW);
        digitalWrite(LED4, LOW);
    }
    else if ((LDRvalue < 411) & (LDRvalue >= 206))
    {
        digitalWrite(LED1, HIGH);
        digitalWrite(LED2, HIGH);
        digitalWrite(LED3, HIGH);
        digitalWrite(LED4, LOW);
    }
    else if (LDRvalue < 205)
    {
        digitalWrite(LED1, HIGH);
        digitalWrite(LED2, HIGH);
        digitalWrite(LED3, HIGH);
        digitalWrite(LED4, HIGH);
    }

    if (temp >= threshold) //temperature control
    {
        digitalWrite(fan, HIGH);
    }
    else if (temp < threshold)
    {
        digitalWrite(fan, LOW);
    }
}

void remotemode() // remote function
{
    digitalWrite(LED1, LOW);
    digitalWrite(LED2, LOW);
    digitalWrite(LED3, LOW);
    digitalWrite(LED4, LOW);

    digitalWrite(fan, LOW);
    digitalWrite(Wpump, LOW);
    digitalWrite(LEDalrm, LOW);
    digitalWrite(buzzer, LOW);

    if (BT.available() > 0)
    {
        state = BT.read(); //transfer data sent by App to a local variable
    }

    if (state == 'D') //actuators operation according to orders received
    {
        digitalWrite(LED1, LOW);
    }
    else if (state == 'C')
    {
        digitalWrite(LED1, HIGH);
    }
    else if (state == 'F')
    {
        digitalWrite(LED2, LOW);
    }
    else if (state == 'E')
    {
        digitalWrite(LED2, HIGH);
    }
    else if (state == 'H')
    {
        digitalWrite(LED3, LOW);
    }
    else if (state == 'G')
    {
        digitalWrite(LED3, HIGH);
    }
    else if (state == 'J')
    {
        digitalWrite(LED4, LOW);
    }
    else if (state == 'I')
    {
        digitalWrite(LED4, HIGH);
    }
    else if (state == 'L')
    {
        digitalWrite(fan, LOW);
    }
    else if (state == 'K')
    {
        digitalWrite(fan, HIGH);
    }
    else if (state == 'N')
    {
        digitalWrite(Wpump, LOW);
    }
    else if (state == 'M')
    {
        digitalWrite(Wpump, HIGH);
    }

    if (state == 'O')
    {
        digitalWrite(LED1, HIGH);
        digitalWrite(LED2, HIGH);
        digitalWrite(LED3, HIGH);
        digitalWrite(LED4, HIGH);
    }
    else if (state == 'P')
    {
        digitalWrite(LED1, LOW);
        digitalWrite(LED2, LOW);
        digitalWrite(LED3, LOW);
        digitalWrite(LED4, LOW);
    }
}

In future, when posting a question, please also list WHICH libraries you are using. e.g. there is more than one LiquidCrystal_I2C library... and probably only one right one. Also, that will only be part of the error message. Give the entire message - as the end bit isn't of much use!