#include <Keypad.h>

const byte ROWS = 2; //four rows
const byte COLS = 2; //three columns
char keys[ROWS][COLS] = {
{'a','b'},
{'c','d'},
};
byte rowPins[ROWS] = {16,17}; //connect to the row pinouts of the kpd
byte colPins[COLS] = {18, 2}; //connect to the column pinouts of the kpd

Keypad kpd = Keypad( makeKeymap(keys), rowPins, colPins, ROWS, COLS );

unsigned long loopCount;
unsigned long startTime;
String msg;


void setup() {
    Serial.begin(9600);
    loopCount = 0;
    startTime = millis();
    msg = "";
}


void loop() {
    loopCount++;
    if ( (millis()-startTime)>5000 ) {
        Serial.print("Average loops per second = ");
        Serial.println(loopCount/5);
        startTime = millis();
        loopCount = 0;
    }

    // Fills kpd.key[ ] array with up-to 10 active keys.
    // Returns true if there are ANY active keys.
    if (kpd.getKeys())
    {
        for (int i=0; i<LIST_MAX; i++)   // Scan the whole key list.
        {
            if ( kpd.key[i].stateChanged )   // Only find keys that have changed state.
            {
                switch (kpd.key[i].kstate) {  // Report active key state : IDLE, PRESSED, HOLD, or RELEASED
                    case PRESSED:
                    msg = " PRESSED.";
                break;
                    case HOLD:
                    msg = " HOLD.";
                break;
                    case RELEASED:
                    msg = " RELEASED.";
                break;
                    case IDLE:
                    msg = " IDLE.";
                }
                Serial.print("Key ");
                Serial.print(kpd.key[i].kchar);
                Serial.println(msg);
            }
        }
    }
}  // End loop