int leftforward=A0;
int rightforward=4;
int leftbackward=A2;
int rightbackward=2;

int leftin=7;
int rightin=5;
int frontin=6;

int frontvalue;
int leftvalue;
int rightvalue;

void setup() {
  // put your setup code here, to run once:
  pinMode(leftforward,OUTPUT);
  pinMode(rightforward,OUTPUT);
  pinMode(leftbackward,OUTPUT);
  pinMode(rightbackward,OUTPUT);
  pinMode(leftin,INPUT_PULLUP);
  pinMode(frontin,INPUT_PULLUP);
  pinMode(rightin,INPUT_PULLUP);
  frontvalue=digitalRead(frontin);
}

void allstop()
{
  digitalWrite(leftforward,LOW);
  digitalWrite(rightforward,LOW);
  digitalWrite(leftbackward,LOW);
  digitalWrite(rightbackward,LOW);
}

void left()
{
  digitalWrite(leftforward,LOW);
  digitalWrite(leftbackward,HIGH);
  digitalWrite(rightforward,HIGH);
  digitalWrite(rightbackward,LOW);
}

void right()
{
  digitalWrite(leftforward,HIGH);
  digitalWrite(leftbackward,LOW);
  digitalWrite(rightforward,LOW);
  digitalWrite(rightbackward,HIGH);
}

void forward()
{
  digitalWrite(leftforward,HIGH);
  digitalWrite(leftbackward,LOW);
  digitalWrite(rightforward,HIGH);
  digitalWrite(rightbackward,LOW);
}

void loop() {
  // put your main code here, to run repeatedly:
  if(frontvalue==0)
  {
    allstop();
    leftvalue=digitalRead(leftin);
    rightvalue=digitalRead(rightin);
    if(leftvalue==0)
    {
      right();
    }
    else if(rightvalue==0)
    {
      left();
    }
    else
    {
      allstop();
    }
  }
  else
  {
    forward();
  }
  frontvalue=digitalRead(frontin);
}