// instead of  String  you can use  char*
#include <LiquidCrystal.h>
LiquidCrystal lcd(12,11,10,9,8,7);
int button1 = 1;
int button2 = 2;
int button3 = 3;
int m = false;
int x;

void setup() {
  // put your setup code here, to run once:
  lcd.begin(16,2);
  pinMode(button1, INPUT_PULLUP);
  pinMode(button2, INPUT_PULLUP);
  pinMode(button3, INPUT_PULLUP);
}

void loop() {
  // put your main code here, to run repeatedly:
  int buttonState1 = digitalRead(button1);
  int buttonState2 = digitalRead(button2);
  int buttonState3 = digitalRead(button3);

  if(buttonState1 == LOW & m == false){
    lcd.setCursor(0,0);
    m = !m;
    x++;
    delay(300);
  }
  if(buttonState2 == LOW & m == false){
    lcd.setCursor(0,0);
    m = !m;
    x--;
    delay(300);
  }
  if(buttonState3 == LOW & m == false){
    lcd.setCursor(0,0);
    m = !m;
    x = 0;
    delay(300);
  }

  buttonState1 = digitalRead(button1);
  buttonState2 = digitalRead(button2);
  buttonState3 = digitalRead(button3);

  if(buttonState1 == HIGH & m == true){
    if(buttonState2 == HIGH & m == true){
      if(buttonState3 == HIGH & m == true){
        m = !m;
        lcd.clear();
        delay(300);
      }
    }
  }
  lcd.setCursor(0,0);
  lcd.print(x);
}