'PINC' was not declared in this scope

Hi everyone,
I've tried the rotary encoder demo code, but it get an error.
Any idea how to fix this?
Thanks in advance
Error at line: old_AB |= ( ENC_PORT & 0x03 ); //add current state

Arduino: 1.5.6-r2 (Windows 8), Board: "Arduino Due (Programming Port)"

rotary.ino: In function 'int8_t read_encoder()':
rotary:37: error: 'PINC' was not declared in this scope

full code

/* Rotary encoder read example */
#define ENC_A 14
#define ENC_B 15
#define ENC_PORT PINC
 
void setup()
{
  /* Setup encoder pins as inputs */
  pinMode(ENC_A, INPUT);
  digitalWrite(ENC_A, HIGH);
  pinMode(ENC_B, INPUT);
  digitalWrite(ENC_B, HIGH);
  Serial.begin (115200);
  Serial.println("Start");
}
 
void loop()
{
 static uint8_t counter = 0;      //this variable will be changed by encoder input
 int8_t tmpdata;
 /**/
  tmpdata = read_encoder();
  if( tmpdata ) {
    Serial.print("Counter value: ");
    Serial.println(counter, DEC);
    counter += tmpdata;
  }
}
 
/* returns change in encoder state (-1,0,1) */
int8_t read_encoder()
{
  static int8_t enc_states[] = {0,-1,1,0,1,0,0,-1,-1,0,0,1,0,1,-1,0};
  static uint8_t old_AB = 0;
  /**/
  old_AB <<= 2;                   //remember previous state
 old_AB |= ( ENC_PORT & 0x03 ); //add current state
  return ( enc_states[( old_AB & 0x0f )]);
}

The compiler has no idea what "PINC" is, it is not declared anywhere.
I think it is the input register of port 'C', but that is for ATmega chips and you are using the Due.
Is there a rotary encoder library that also works on the Due ?

more pinc: Aerosmith - Pink - YouTube

It compiles without error on my Arduino Uno, so the hiccup might be with the use of the Due board.