int a=13; 
int b=12;
int c=11;
int d=10;
int e=9;
int f=8;
int g=7;

void setup() {
  // put your setup code here, to run once:
  pinMode(a, OUTPUT);
  pinMode(b, OUTPUT);
  pinMode(c, OUTPUT);
  pinMode(d, OUTPUT);
  pinMode(e, OUTPUT);
  pinMode(f, OUTPUT);
  pinMode(g, OUTPUT);

}

void loop() {
  // put your main code here, to run repeatedly:
  //0
  int expression;
  for(int i=0;i<10;i=i+2){
    expression =i;
  
  switch(expression) {
    case 0:
      digitalWrite(a,0);
    digitalWrite(b,0);
    digitalWrite(c,0);
    digitalWrite(d,0);
    digitalWrite(e,0);
    digitalWrite(f,0);
    digitalWrite(g,1);
    delay(500);
    // code block
      break;
    case 1:
      digitalWrite(a,1);
    digitalWrite(b,0);
    digitalWrite(c,0);
    digitalWrite(d,1);
    digitalWrite(e,1);
    digitalWrite(f,1);
    digitalWrite(g,1);
    delay(500);
    // code block
      break;
    case 2:
      digitalWrite(a,0);
      digitalWrite(b,0);
      digitalWrite(c,1);
      digitalWrite(d,0);
      digitalWrite(e,0);
      digitalWrite(f,1);
      digitalWrite(g,0);
      delay(500);
    // code block
      break;
    case 3:
      digitalWrite(a,0);
      digitalWrite(b,0);
      digitalWrite(c,0);
      digitalWrite(d,0);
      digitalWrite(e,1);
      digitalWrite(f,1);
      digitalWrite(g,0);
      delay(500);
    // code block
      break;
    case 4:
      digitalWrite(a,1);
      digitalWrite(b,0);
      digitalWrite(c,0);
      digitalWrite(d,1);
      digitalWrite(e,1);
      digitalWrite(f,0);
      digitalWrite(g,0);
      delay(500);
    // code block
      break;
    case 5:
      digitalWrite(a,0);
      digitalWrite(b,1);
      digitalWrite(c,0);
      digitalWrite(d,0);
      digitalWrite(e,1);
      digitalWrite(f,0);
      digitalWrite(g,0);
      delay(500);
    // code block
      break;
    case 6:
      digitalWrite(a,0);
      digitalWrite(b,1);
      digitalWrite(c,0);
      digitalWrite(d,0);
      digitalWrite(e,0);
      digitalWrite(f,0);
      digitalWrite(g,0);
      delay(500);
    // code block
      break;
    case 7:
      digitalWrite(b,0);
      digitalWrite(c,0);
      digitalWrite(d,1);
      digitalWrite(a,0);
      digitalWrite(e,1);
      digitalWrite(f,1);
      digitalWrite(g,1);
      delay(500);
    // code block
      break;
    case 8:
      digitalWrite(b,0);
      digitalWrite(c,0);
      digitalWrite(d,0);
      digitalWrite(a,0);
      digitalWrite(e,0);
      digitalWrite(f,0);
      digitalWrite(g,0);
      delay(500);
    // code block
      break;
    case 9:
      digitalWrite(a,0);
      digitalWrite(b,0);
      digitalWrite(c,0);
      digitalWrite(d,0);
      digitalWrite(e,1);
      digitalWrite(f,0);
      digitalWrite(g,0);
      delay(500);
    // code block
      break;
    
    }
  }
}