I’d like to do a countdown. To do this I would like to enter with a keyboard a membrane a number on a 16x2 lcd screen and that this makes a timer up to 0. Currently what I can not understand and how to write the number for my timer and subtract it.
If you have leads I am taker. Thank you good day 
Found with Google search for "countdown lcd keypad arduino". If these do not help, describe what you want in better detail.
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With these links I tried to put a 3 digit number in a tank then that one subtracts 0 once these 3 digits written on my lcd screen. What I can’t do is how to get my number to 0 now. Here’s my code for more explanation
Thank you
#include <Wire.h>
#include <DS3231.h>
#include <LiquidCrystal.h>
#include <Keypad.h>
int tempPin = 0;
LiquidCrystal lcd(7, 8, 9, 10, 11, 12);
int calibrationTime = 30;
long unsigned int lowIn;
int inputPin = 3;
int pirState = LOW;
int val = 0;
const byte ROWS = 4; //four rows
const byte COLS = 4; //four columns
//define the cymbols on the buttons of the keypads
char hexaKeys[ROWS][COLS] = {
{'1', '2', '3'}
};
byte rowPins[ROWS] = {13};
byte colPins[COLS] = {5, 4, 2 };
char timer[3];
int number= 0;
//initialize an instance of class NewKeypad
Keypad customKeypad = Keypad( makeKeymap(hexaKeys), rowPins, colPins, ROWS, COLS);
void setup(){
lcd.begin(16, 2);
delay(2000);
lcd.clear();
lcd.clear();
Serial.begin(9600);
pinMode(inputPin, INPUT);
}
void loop()
{
lcd.setCursor(0,0);
lcd.print("Bomb explosion :");
while(number< 3){
lcd.setCursor(nombre + 0,1);
lcd.cursor();
char customKey = customKeypad.getKey();
customKey == NO_KEY;
if(customKey != NO_KEY){
if((customKey != '*') && (customKey != '#')){
lcd.print(customKey);
Serial.println(customKey);
timer[number] = customKey;
number++;
}
}
}
while(number== 3){
int sous = 1;
number= (timer - sous);
lcd.print(timer[number]);
}
}