Arduino Gps Clock

#include <TinyGPS++.h>
TinyGPSPlus gps;
int d1a = 12;
int d1b = 11;
int d1c = 10;
int d1d = 9;
int d2a = 7;
int d2b = 6;
int d2c = 5;
int d2d = 4;
int d3a = 22;
int d3b = 23;
int d3c = 24;
int d3d = 25;
int d4a = 26;
int d4b = 27;
int d4c = 28;
int d4d = 29;
int ampmled = 30;
int hr = 0;
int mn = 0;
int timezonehr = -6; //Timezone hour offset
int timezonemn = 0;  //Timezone minute offset
int numbers[][4] =   //Display codes
{
  {0,0,0,0}, // 0
  {0,0,0,1}, // 1
  {1,0,0,0}, // 2
  {1,0,0,1}, // 3
  {0,1,0,0}, // 4
  {0,1,0,1}, // 5
  {1,1,0,0}, // 6
  {1,1,0,1}, // 7
  {0,0,1,0}, // 8
  {0,0,1,1}, // 9
  {1,1,1,1}  // Clear
};
int num[4];
void disp(int dispnum,int numtodisplay){
    for (int x = 0; x < 4; x++){
      num[x] = numbers[numtodisplay][x];
    }
    if (dispnum == 1){
     if (num[0] == 1){
       digitalWrite(d1a, HIGH);
     }
     else{
       digitalWrite(d1a, LOW);
     }
     if (num[1] == 1){
       digitalWrite(d1b, HIGH);
     }
     else{
       digitalWrite(d1b, LOW);
     }
     if (num[2] == 1){
       digitalWrite(d1c, HIGH);
     }
     else{
       digitalWrite(d1c, LOW);
     }
     if (num[3] == 1){
       digitalWrite(d1d, HIGH);
     }
     else{
       digitalWrite(d1d, LOW);
     }
    }
    if (dispnum == 2){
     if (num[0] == 1){
       digitalWrite(d2a, HIGH);
     }
     else{
       digitalWrite(d2a, LOW);
     }
     if (num[1] == 1){
       digitalWrite(d2b, HIGH);
     }
     else{
       digitalWrite(d2b, LOW);
     }
     if (num[2] == 1){
       digitalWrite(d2c, HIGH);
     }
     else{
       digitalWrite(d2c, LOW);
     }
     if (num[3] == 1){
       digitalWrite(d2d, HIGH);
     }
     else{
       digitalWrite(d2d, LOW);
     }
    }
    if (dispnum == 3){
     if (num[0] == 1){
       digitalWrite(d3a, HIGH);
     }
     else{
       digitalWrite(d3a, LOW);
     }
     if (num[1] == 1){
       digitalWrite(d3b, HIGH);
     }
     else{
       digitalWrite(d3b, LOW);
     }
     if (num[2] == 1){
       digitalWrite(d3c, HIGH);
     }
     else{
       digitalWrite(d3c, LOW);
     }
     if (num[3] == 1){
       digitalWrite(d3d, HIGH);
     }
     else{
       digitalWrite(d3d, LOW);
     }
    }
    if (dispnum == 4){
     if (num[0] == 1){
       digitalWrite(d4a, HIGH);
     }
     else{
       digitalWrite(d4a, LOW);
     }
     if (num[1] == 1){
       digitalWrite(d4b, HIGH);
     }
     else{
       digitalWrite(d4b, LOW);
     }
     if (num[2] == 1){
       digitalWrite(d4c, HIGH);
     }
     else{
       digitalWrite(d4c, LOW);
     }
     if (num[3] == 1){
       digitalWrite(d4d, HIGH);
     }
     else{
       digitalWrite(d4d, LOW);
     }
    }
}
void setup() {
  // put your setup code here, to run once:
  pinMode(d1a, OUTPUT);
  pinMode(d1b, OUTPUT);
  pinMode(d1c, OUTPUT);
  pinMode(d1d, OUTPUT);
  pinMode(d2a, OUTPUT);
  pinMode(d2b, OUTPUT);
  pinMode(d2c, OUTPUT);
  pinMode(d2d, OUTPUT);
  pinMode(d3a, OUTPUT);
  pinMode(d3b, OUTPUT);
  pinMode(d3c, OUTPUT);
  pinMode(d3d, OUTPUT);
  pinMode(d4a, OUTPUT);
  pinMode(d4b, OUTPUT);
  pinMode(d4c, OUTPUT);
  pinMode(d4d, OUTPUT);
  pinMode(ampmled, OUTPUT);
  Serial.begin(9600);
  Serial3.begin(9600);
}
uint32_t timer = millis();
void loop() {
  // put your main code here, to run repeatedly:
  while (Serial3.available()) {
      gps.encode(Serial3.read());
  }
  if (timer > millis())  timer = millis();
  if (millis() - timer > 500) {
    timer = millis();
    hr = gps.time.hour();
    mn = gps.time.minute();
    //hr = 0; //DEBUG
    //mn = 0; //DEBUG
    mn = mn + timezonemn;
    if (mn > 59) {
      mn = mn - 60;
      hr = hr + 1;
    }
    else {
      if (mn < 0) {
        mn = mn + 60;
        hr = hr - 1;
      }
    }
    hr = hr + timezonehr;
    if (hr > 23) {
      hr = hr - 24;
    }
    else {
      if (hr < 0) {
        hr = hr + 24;
      }
    }
    if (hr > 12) {
      hr = hr - 12;
      digitalWrite(ampmled, LOW);
    }
    else {
      digitalWrite(ampmled, HIGH);
    }
    if (hr == 0) {
      hr = 12;
    }
    disp(1, int(hr / 10));
    disp(2, int(hr % 10));
    disp(3, int(mn / 10));
    disp(4, int(mn % 10));
  }
}