LCD Screen countdown timer problem and input problem

Projects Programming
3

Thanks for trying to help me Boguz, but I cant get it working on that way either. it just makes my whole screen flickering and the time rushing down as if the delay is only 1ms.
I guess i am failing to put the commands in a good order/way into my code.

#include <LiquidCrystal.h>
#include <SimpleTimer.h> 

LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
  int plusPin = 6;
  int minPin = 7;
  int I=0;
  int U=0;
  int T=0;
  long previousMillis = 0;
  long interval = 1000;
void setup() {
  pinMode(plusPin, INPUT);
  pinMode(minPin, INPUT);
  lcd.begin(16, 2);
  lcd.setCursor(0,0);
  lcd.print("Verkeerstelling");
  
  delay(1000); 
}

void loop() 
  {
  lcd.clear();
  
  if (plusPin, LOW) 
  {
  (I++);
  }
  if (minPin, LOW) 
  {
  (U++);
  }
  lcd.setCursor(0,0);
  lcd.print("In: ");
  lcd.setCursor(4,0);
  lcd.print(I);
  lcd.setCursor(8,0);
  lcd.print("Uit: ");
  lcd.setCursor(13,0);
  lcd.print(U);
  T = (I-U);
  lcd.setCursor(0,1);
  lcd.print("Totaal: ");
  lcd.setCursor(8,1);
  lcd.print(T);
  lcd.setCursor(13, 1);

  int n = 0;
  for ( n = 110; n > 0; n--) 
    {
    lcd.setCursor(13, 1);
    //delay(1000);
    unsigned long currentMillis = millis();
    if(currentMillis - previousMillis > interval) {
      previousMillis = currentMillis;
    
    if (lcd.print(n));
    
}