Digital Voltmeter ARDUINO

#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27,16,2);

double sensorValue1 = 0;
double sensorValue2 = 0;
int crosscount = 0;
int climb_flag = 0;
int val[100];
int max_v = 0;
double VmaxD = 0;
double VeffD = 0;
double Veff = 0;
int xCoord = 0;

void setup() {
  Serial.begin(9600);
  lcd.init();
  lcd.backlight();
  lcd.clear();
  lcd.setCursor(0,0);
  lcd.print("Daradici Levente");
  lcd.setCursor(2,1);
  lcd.print("AC Voltmeter");
  delay(3000);
  lcd.clear();
}

void loop() {

  for ( int i = 0; i < 100; i++ ) {
    sensorValue1 = analogRead(A0);
    if (analogRead(A0) > 511) {
      val[i] = sensorValue1;
    }
    else {
      val[i] = 0;
    }
    delay(1);
  }

  max_v = 0;

  for ( int i = 0; i < 100; i++ )
  {
    if ( val[i] > max_v )
    {
      max_v = val[i];
    }
    val[i] = 0;
  }
  if (max_v != 0) {


    VmaxD = max_v;
    VeffD = VmaxD / sqrt(2);
    Veff = (((VeffD - 420.76) / -90.24) * -210.2) + 210.2;
  }
  else {
    Veff = 0;
  }
  Serial.print("Voltage: ");
  Serial.println(Veff);
  VmaxD = 0;

  if (Veff < 1000) { xCoord = 8; }
  if (Veff < 100) { xCoord = 9; }
  if (Veff < 10) { xCoord = 10; }
  lcd.clear();
  lcd.setCursor(xCoord,1);
  lcd.print(Veff);
  lcd.setCursor(15,1);
  lcd.print("V");
  delay(500);

}