cal.ino

#include <LiquidCrystal.h>
#include <Keypad.h>

const byte ROWS = 4;
const byte COLS = 4;

char keys[ROWS][COLS] = {
  { '1', '2', '3', 'A' },
  { '4', '5', '6', 'B' },
  { '7', '8', '9', 'C' },
  { '*', '0', '#', 'D' }
};

byte rowPins[ROWS] = { 0, 1, 2, 3 };
byte colPins[COLS] = { 4, 5, 6, 7 };
Keypad kpd = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

const int rs = 8, en = 9, d4 = 10, d5 = 11, d6 = 12, d7 = 13;
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);

long Num1, Num2, Number;
char key, action;
boolean result = false;

void setup() {
  lcd.begin(16, 2);
  lcd.setCursor(0, 0);
  lcd.print("Calculator");
  delay(1000);
  lcd.setCursor(0, 1);
  lcd.print("Loading...");

  delay(2000);
  lcd.clear();
}

void loop() {
  key = kpd.getKey();

  if (key != NO_KEY)
    DetectButtons();
  if (result == true)
    CalculateResult();
  DisplayResult();
}

void DetectButtons() {
  lcd.clear();
  if (key == '*') {
    Number = Num1 = Num2 = 0;
    result = false;
  }

  if (key == '1') {
    if (Number == 0)
      Number = 1;
    else
      Number = (Number * 10) + 1;
  }
  if (key == '4') {
    if (Number == 0)
      Number = 4;
    else
      Number = (Number * 10) + 4;
  }
  if (key == '7') {
    if (Number == 0)
      Number = 7;
    else
      Number = (Number * 10) + 7;
  }
  if (key == '0') {
    if (Number == 0)
      Number = 0;
    else
      Number = (Number * 10) + 0;
  }
  if (key == '2') {
    if (Number == 0)
      Number = 2;
    else
      Number = (Number * 10) + 2;
  }
  if (key == '5') {
    if (Number == 0)
      Number = 5;
    else
      Number = (Number * 10) + 5;
  }
  if (key == '8') {
    if (Number == 0)
      Number = 8;
    else
      Number = (Number * 10) + 8;
  }
  if (key == '#') {
    Num2 = Number;
    result = true;
  }
  if (key == '3') {
    if (Number == 0)
      Number = 3;
    else
      Number = (Number * 10) + 3;
  }
  if (key == '6') {
    if (Number == 0)
      Number = 6;
    else
      Number = (Number * 10) + 6;
  }
  if (key == '9') {
    if (Number == 0)
      Number = 9;
    else
      Number = (Number * 10) + 9;
  }
  if (key == 'A' || key == 'B' || key == 'C' || key == 'D') {
    Num1 = Number;
    Number = 0;
    if (key == 'A') { action = '+'; }
    if (key == 'B') { action = '-'; }
    if (key == 'C') { action = '*'; }
    if (key == 'D') { action = '/'; }
    delay(100);
  }
}

void CalculateResult() {
  if (action == '+')
    Number = Num1 + Num2;
  if (action == '-')
    Number = Num1 - Num2;
  if (action == '*')
    Number = Num1 * Num2;
  if (action == '/')
    Number = Num1 / Num2;
}

void DisplayResult() {
  lcd.setCursor(0, 0);
  lcd.print(Num1);
  lcd.print(action);
  lcd.print(Num2);
  if (result == true) {
    lcd.print(" = ");
    lcd.setCursor(0, 1);
    lcd.print(Number);
  }
}