Need help on robot programming!

Using Arduino Programming Questions
1

Hello everyone! I made a simple robot using the guide here and I have a problem with it.

I am not good at programming Arduino, and I am using the code from that guide that works with my HC-SR04 ultrasonic sensor. However, I want my robot back up and turn left when it sees an object, instead of just turning left.

Here's the code I'm trying to modify:

#include <Servo.h>

// create servo objects
Servo leftMotor;
Servo rightMotor;

const int serialPeriod = 250;       // only print to the serial console every 1/4 second
unsigned long timeSerialDelay = 0;

const int loopPeriod = 20;          // a period of 20ms = a frequency of 50Hz
unsigned long timeLoopDelay   = 0;

// specify the trig & echo pins used for the ultrasonic sensors
const int ultrasonic2TrigPin = 8;
const int ultrasonic2EchoPin = 9;

int ultrasonic2Distance;
int ultrasonic2Duration;

// define the states
#define DRIVE_FORWARD     0
#define TURN_LEFT         1

int state = DRIVE_FORWARD; // 0 = drive forward (DEFAULT), 1 = turn left

void setup()
{
  Serial.begin(9600);

  // ultrasonic sensor pin configurations
  pinMode(ultrasonic2TrigPin, OUTPUT);
  pinMode(ultrasonic2EchoPin, INPUT);
  
  leftMotor.attach(13);
  rightMotor.attach(12);
}


void loop()
{
  debugOutput(); // prints debugging messages to the serial console
  
  if(millis() - timeLoopDelay >= loopPeriod)
  {
      readUltrasonicSensors(); // read and store the measured distances
      
      stateMachine();
      
      timeLoopDelay = millis();
  }
}


void stateMachine()
{
  if(state == DRIVE_FORWARD) // no obstacles detected
  {
      if(ultrasonic2Distance > 6 || ultrasonic2Distance < 0) // if there's nothing in front of us (note: ultrasonicDistance will be negative for some ultrasonics if there's nothing in range)
      {
          // drive forward
          rightMotor.write(180);
          leftMotor.write(0);
      }
      else // there's an object in front of us
      {
          state = TURN_LEFT;
      }
  }
  else if(state == TURN_LEFT) // obstacle detected -- turn left
  {
      unsigned long timeToTurnLeft = 1100; // it takes around 1.1 seconds to turn 90 degrees
      
      unsigned long turnStartTime = millis(); // save the time that we started turning

      while((millis()-turnStartTime) < timeToTurnLeft) // stay in this loop until timeToTurnLeft (1.1 seconds) has elapsed
      {
          // turn left
          rightMotor.write(180);
          leftMotor.write(180);
      }
      
      state = DRIVE_FORWARD;
  }
}


void readUltrasonicSensors()
{
  // ultrasonic 2
  digitalWrite(ultrasonic2TrigPin, HIGH);
  delayMicroseconds(10);                  // must keep the trig pin high for at least 10us
  digitalWrite(ultrasonic2TrigPin, LOW);
  
  ultrasonic2Duration = pulseIn(ultrasonic2EchoPin, HIGH);
  ultrasonic2Distance = (ultrasonic2Duration/2)/29;
}


void debugOutput()
{
  if((millis() - timeSerialDelay) > serialPeriod)
  {
      Serial.print("ultrasonic2Distance: ");
      Serial.print(ultrasonic2Distance);
      Serial.print("cm");
      Serial.println();
      
      timeSerialDelay = millis();
  }
}

That code is from the guide I am using.

I need the modified code ASAP!

Thanks in advance!

Moderator edit:
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</mark> <mark>[/code]</mark> <mark>
tags added.

2 
  if(state == DRIVE_FORWARD) // no obstacles detected
  {
      if(ultrasonic2Distance > 6 || ultrasonic2Distance < 0) // if there's nothing in front of us (note: ultrasonicDistance will be negative for some ultrasonics if there's nothing in range)
      {
          // drive forward
          rightMotor.write(180);
          leftMotor.write(0);
      }
      else // there's an object in front of us
      {
          state = TURN_LEFT;
      }
  }
  else if(state == TURN_LEFT) // obstacle detected -- turn left
  {
      unsigned long timeToTurnLeft = 1100; // it takes around 1.1 seconds to turn 90 degrees
      
      unsigned long turnStartTime = millis(); // save the time that we started turning

      while((millis()-turnStartTime) < timeToTurnLeft) // stay in this loop until timeToTurnLeft (1.1 seconds) has elapsed
      {
          // turn left
          rightMotor.write(180);
          leftMotor.write(180);
      }
      
      state = DRIVE_FORWARD;
  }
}

There is the relevant bit. You only have the option of going forward or turning left as written. So your first job is to add a case for reverse. You can use the case for forward as a model.