Question about millis()

i’m using a code for right to my led display using millis.
my question is what happen after approximately 50 days.

the code is :

/*

*/
#include <LedDisplay.h>

// Define pins for the LED display.
// You can change these, just re-wire your board:
#define dataPin 6 // connects to the display’s data in
#define registerSelect 7 // the display’s register select pin
#define clockPin 8 // the display’s clock pin
#define enable 9 // the display’s chip enable pin
#define reset 10 // the display’s reset pin
#define displayLength 8 // number of bytes needed to pad the string
// create am instance of the LED display:
LedDisplay myDisplay = LedDisplay(dataPin, registerSelect, clockPin,
enable, reset, displayLength);

int lcdstate = 0; //estado do LCD
long previousMillis = 0;
long interval = 1000;
int brightness = 15; // screen brightness
char open = {’ ‘,‘O’,‘p’,‘e’,‘n’,’ ‘,’ ‘,’ ‘};
char door = {’ ‘,‘D’,‘o’,‘o’,‘r’,’ ‘,’ ‘,’ ‘,};
//char del={’ ‘,’ ‘,’ ‘,’ ‘,’ ‘,’ ‘,’ ‘,’ ',};
void setup() {
Serial.begin(9600);

// initialize the display library:
myDisplay.begin();
myDisplay.setString(“Open”);
myDisplay.home();
myDisplay.setBrightness(brightness);
}

void loop() {
if (millis()- previousMillis > interval) {
previousMillis = millis();
if (lcdstate == 0){
myDisplay.home();
for (int thisPosition = 0; thisPosition < 8; thisPosition++)
{
myDisplay.write(open[thisPosition]);
}
lcdstate = 1;
}
else {
myDisplay.home();
for (int thisPosition = 0; thisPosition < 8; thisPosition++)
{
myDisplay.write(door[thisPosition]);
}
lcdstate = 0;
}

}
}

Change this...

long previousMillis = 0;
long interval = 1000;

...to this...

unsigned long previousMillis = 0;
unsigned long interval = 1000;

...and you should be good to go. I believe you can test by using "unsigned short" instead of "unsigned long". The roll-over should occur in just over one minute.

tks for help