#include <LiquidCrystal.h>
#include <Keypad.h>
 
 
LiquidCrystal lcd(7, 8, 9, 10, 11 , 12);
const byte ROWS = 4; 
const byte COLS = 4; 
char keys[ROWS][COLS] = {
  {'1','2','3','+'},
  {'4','5','6','-'},
  {'7','8','9','*'},
  {'X','0','=','/'},
};
byte rowPins[ROWS] = {53,51,49,47}; //connect to row pinouts 
byte colPins[COLS] = {45,43,41,39}; //connect to column pinouts
Keypad myKeypad = Keypad( makeKeymap(keys), rowPins, colPins, ROWS, COLS );
 
 
//variables declaration
boolean valOnePresent = false;
boolean next = false;
boolean final = false;
String num1, num2;
int ans;
char op;
 
void setup(){
  lcd.begin(16,2);
  lcd.setCursor(0,0);
  lcd.print("Debit Volumique");
  delay(6000);
  lcd.clear(); //clears the LCD screen and positions the cursor in the upper-left corner. 
}    
 
void loop(){
  char key = myKeypad.getKey();
 
  if (key != NO_KEY && (key=='1'||key=='2'||key=='3'||key=='4'||key=='5'||key=='6'||key=='7'||key=='8'||key=='9'||key=='0')){
    if (valOnePresent != true){
      num1 = num1 + key;
      int numLength = num1.length();
      lcd.setCursor(15 - numLength, 0); //to adjust one whitespace for operator
      lcd.print(num1);
    }
    else {
      num2 = num2 + key;
      int numLength = num2.length();
      lcd.setCursor(15 - numLength, 1);
      lcd.print(num2);
      final = true;
    }
  }
 
  else if (valOnePresent == false && key != NO_KEY && (key == '/' || key == '*' || key == '-' || key == '+')){
    if (valOnePresent == false){
      valOnePresent = true;
      op = key;
      lcd.setCursor(15,0); //operator on right corner
      lcd.print(op);
    }
  }
 
  else if (final == true && key != NO_KEY && key == '='){
    if (op == '+'){
      ans = num1.toInt() + num2.toInt();
    }
    else if (op == '-'){
      ans = num1.toInt() - num2.toInt();
    }
    else if (op == '*'){
      ans = num1.toInt() * num2.toInt();
    }
    else if (op == '/'){
      ans = num1.toInt() / num2.toInt();
    }    
      lcd.clear();
      lcd.setCursor(15,0);
      lcd.autoscroll();
      lcd.print(ans);
      lcd.noAutoscroll();
  }
  else if (key != NO_KEY && key == 'X'){
    lcd.clear();
    valOnePresent = false;
    final = false;
    num1 = "";
    num2 = "";
    ans = 0;
    op = ' ';
  }
}

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