Arduino Project 001v2 7 segment display 4 digits

//arduino 4 digit 7 segment project
#define DIGIT_ON  HIGH
#define DIGIT_OFF  LOW

int time = 10;

int x=100;

int a = 1;
int b = 2;
int c = 3;
int d = 4;
int e = 5;
int f = 6;
int g = 7;
//segments
char seg[]= {a,b,c,d,e,f,g};
//numbers and others
int num[10][7] = {{1,1,1,1,1,1,0}, //0
         {0,0,1,1,0,0,0}, //1
         {1,1,0,1,1,0,1}, //2
         {0,1,1,1,1,0,1}, //3
         {0,0,1,1,0,1,1}, //4
         {0,1,1,0,1,1,1}, //5
         {1,1,1,0,1,1,1}, //6
         {0,0,1,1,1,0,0}, //7
         {1,1,1,1,1,1,1}, //8
         {0,0,1,1,1,1,1}};//9

int hifen[] =   {0,0,0,0,0,0,1}; //-
int o[] =       {1,1,1,0,0,0,1}; //o

long t,t2; //time of numbers

void setup(){
 pinMode(13, OUTPUT);// 4 digit
 pinMode(12, OUTPUT);// 3 digit
 pinMode(11, OUTPUT);// 2 digit
 pinMode(10, OUTPUT);// 1 digit

 pinMode(g, OUTPUT);
 pinMode(f, OUTPUT);
 pinMode(e, OUTPUT);
 pinMode(d, OUTPUT);
 pinMode(c, OUTPUT);
 pinMode(b, OUTPUT);
 pinMode(a, OUTPUT);
}

void loop(){
  //counter
  for(int i=0; i<10; i++){
    for(int j=0; j<10; j++){
      for(int k=0; k<10; k++){
        for(int l=0; l<10; l++){
          t=millis();
          while(t2<(t+1000)){ //1s, podem colocar o contador a correr à velocidade que quiserem
            printNumber(i,3);
            delayMicroseconds(time);
            printNumber(j,2);
            delayMicroseconds(time);
            printNumber(k,1);
            delayMicroseconds(time);
            printNumber(l,0);
            delayMicroseconds(time);
            t2=millis();
          }
        }
      }
    }
  }

  //loop
  /*
  for(int i =0 ; i<8 ; i++){
     lightNumber(o);
     digitalWrite((10),LOW);
     delay(200);
     lightNumber(hifen);
     digitalWrite((11),LOW);
     delay(200);
     lightNumber(hifen);
     digitalWrite((12),LOW);
     delay(200);
     lightNumber(o);
     digitalWrite((13),LOW);
     delay(200);
     lightNumber(hifen);
     digitalWrite((12),LOW);
     delay(200);
     lightNumber(hifen);
     digitalWrite((11),LOW);
     delay(200);

  } */
}

void lightNumber(int c[]){
  clearLeds();
  for(int i=0; i<7; i++){
    if(c[i]==1){
      digitalWrite(seg[i], HIGH);
    }
  }
}

void printNumber(int n, int index){
  clearLeds();
  if(n>=0 && n<=9){
    lightNumber(num[n]);
  }
  digitalWrite((10+index),LOW);
}

void clearLeds(){
  for(int i=0; i<7; i++){
    digitalWrite(seg[i], LOW);
  }
  digitalWrite(13, HIGH);
  digitalWrite(12, HIGH);
  digitalWrite(11, HIGH);
  digitalWrite(10, HIGH);
}