https://www.arduino.cc/en/Guide/Libraries#.UxU8mdzF9H0

#if defined(ARDUINO) && ARDUINO >= 100

#include "Arduino.h"

#else

#include "WProgram.h"

#endif

#include "clsPCA9555.h"

#include "Wire.h"

PCA9555 ioport(0x20);

void setup()

{

ioport.pinMode(8, OUTPUT); //Set GPIOs pinMode LED

ioport.pinMode(15, INPUT);

//Button

}

void loop()

{

if (ioport.digitalRead(ED15) == LOW) {

ioport.digitalWrite(8, LOW);

//Turn off Led

}

if (ioport.digitalRead(ED15) == HIGH) {

ioport.digitalWrite(8, HIGH);

//Turn on Led

}

}