Keypad on pins 11 to 4, on an Arduino Uno

// A 4x4 keypad: sixteen keys on eight pins.
//
//   keypad rows 1..4 -> pins 11, 10, 9, 8   columns 1..4 -> pins 7, 6, 5, 4
//
// The library drives one row at a time and reads the columns: a pressed key
// joins its row to its column, so the row being driven shows up on that
// column. That finds the key with eight wires instead of sixteen.
//
// Click a key on the keypad.

#include <Keypad.h>

const char KEYS[4][4] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7', '8', '9', 'C'},
  {'*', '0', '#', 'D'},
};
byte rowPins[4] = {11, 10, 9, 8};
byte colPins[4] = {7, 6, 5, 4};
Keypad keypad = Keypad(makeKeymap(KEYS), rowPins, colPins, 4, 4);

void setup() {
  Serial.begin(9600);
  Serial.println("UNO is ready! Press a key.");
}

void loop() {
  char key = keypad.getKey();
  if (key) Serial.println(key);
}