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

int lefttrig=10;
int leftecho=9;
int fronttrig=8;
int frontecho=7;
int righttrig=6;
int rightecho=5;

int frontvalue;
int leftvalue;
int rightvalue;
int duration;

void setup() {
  // put your setup code here, to run once:
  pinMode(leftforward,OUTPUT);
  pinMode(rightforward,OUTPUT);
  pinMode(leftbackward,OUTPUT);
  pinMode(rightbackward,OUTPUT);
  pinMode(leftecho,INPUT);
  pinMode(frontecho,INPUT);
  pinMode(rightecho,INPUT);
  pinMode(lefttrig,OUTPUT);
  pinMode(fronttrig,OUTPUT);
  pinMode(righttrig,OUTPUT);  
  frontvalue=distance(fronttrig,frontecho);
  Serial.begin(9600);
}

int distance(int trig,int echo){
  digitalWrite(trig,LOW);
  delayMicroseconds(2);
  digitalWrite(trig,HIGH);
  delayMicroseconds(10);
  digitalWrite(trig,LOW);
  duration=pulseIn(echo,HIGH);
  return duration/58;
}
void allstop()
{
  digitalWrite(leftforward,LOW);
  digitalWrite(rightforward,LOW);
  digitalWrite(leftbackward,LOW);
  digitalWrite(rightbackward,LOW);
  Serial.println("Stop");
}

void left()
{
  digitalWrite(leftforward,LOW);
  digitalWrite(leftbackward,HIGH);
  digitalWrite(rightforward,HIGH);
  digitalWrite(rightbackward,LOW);
  Serial.println("Left");
}

void right()
{
  digitalWrite(leftforward,HIGH);
  digitalWrite(leftbackward,LOW);
  digitalWrite(rightforward,LOW);
  digitalWrite(rightbackward,HIGH);
  Serial.println("right");
}

void forward()
{
  digitalWrite(leftforward,HIGH);
  digitalWrite(leftbackward,LOW);
  digitalWrite(rightforward,HIGH);
  digitalWrite(rightbackward,LOW);
  Serial.println("Forward");
}

void loop() {
  // put your main code here, to run repeatedly:
  if(frontvalue<=50)
  {
    allstop();
    leftvalue=distance(lefttrig,leftecho);
    Serial.print("Leftvalue: ");
    Serial.println(leftvalue);
    rightvalue=distance(righttrig,rightecho);
    Serial.print("Rightvalue: ");
    Serial.println(rightvalue);
    if(rightvalue>frontvalue&&rightvalue>=leftvalue)
    {
      right();
    }
    else if(leftvalue>frontvalue)
    {
      left();
    }
    else
    {
      allstop();
    }
  }
  else
  {
    forward();
  }
  delay(250);
  frontvalue=distance(fronttrig,frontecho);
  Serial.print("frontvalue: ");
  Serial.println(frontvalue);
}