#include <Keypad.h>
const byte ROWS = 4;
// four rows const byte
const byte COLS = 4; // four columns
char keys[ROWS][COLS] = {
    {'1', '2', '3', '+'},
    {'4', '5', '6', '-'},
    {'7', '8', '9', '*'},
    {'.', '0', '=', '/'}};
byte rowPins[ROWS] =  {5, 4, 3, 2}; // connect to the row pinouts of the keypad
byte colPins[COLS] =  {A3, A2, A1, A0}; // connect to the column pinouts of the keypad
Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);
int numberArray[10]; // array for storing input numbers from keypad v
void setup()
{
  Serial.begin(9600); // start serial connection for debugging/testing purposes
}
void loop()
{
  char keypressed = keypad.getKey();
  // read the pressed key from the keypad
  if (keypressed != NO_KEY)
  { // if a valid key is pressed
    if (keypressed >= '0' && keypressed <= '9')
    {
      // check if it is a number between 0 and 9
      int numpressed = (int)keypressed - 48; // convert char to int by subtracting 48
      Serial.println(numpressed);            // print out value of numpressed for debugging/testing purposes
      static int i;                          // declare and initialize static variable i to count number of times a valid number is entered
      numberArray[i] = numpressed;           // store number in array at index i
      i++;                                   // increment i
      if (i == 10)
      { // if all 4 numbers are entered
        i = 0;
        // reset counter i to 0
        Serial.println("All numbers entered"); // print out message for debugging/testing purposes
      }
    }
  }
}