Make mobile bluetooth controlled rover using Arduino uno | DIY | Tutorial

Arduino Code:

#include <AFMotor.h>   //import your motor shield library
AF_DCMotor motor1(1,MOTOR12_64KHZ); // set up motors.
AF_DCMotor motor2(2, MOTOR12_8KHZ);
AF_DCMotor motor3(3,MOTOR12_64KHZ); // set up motors.
AF_DCMotor motor4(4, MOTOR12_8KHZ);
char data;

void setup() {
  Serial.begin(9600); // begin serial communitication 
  Serial.println("Motor test!");
  motor3.setSpeed(250); //set the speed of the motors, between 0-255
motor4.setSpeed (250); 
 motor1.setSpeed(250); //set the speed of the motors, between 0-255
motor2.setSpeed (250); 
}

void loop() {

  if(Serial.available()>0)
  {
    data=Serial.read();
    if(data=='8') 
    {
   Serial.println ("I AM MOVING IN FORWARD DIRECTION !" );

    motor1.run(FORWARD); 
    motor2.run(FORWARD); 
    motor3.run(FORWARD); 
    motor4.run(FORWARD); 
   
}
  else if (data=='6') {
   Serial.println ("I JUST TURNED RIGHT !");
   delay (15);
 
  motor1.run(BACKWARD);
 motor2.run(FORWARD); 
  motor3.run(BACKWARD); 
   motor4.run(FORWARD); 
  } 
  else if (data=='4') {
   Serial.println ("I JUST TURNED LEFT !");
   delay (15);
 
   motor1.run(FORWARD);
   motor2.run(BACKWARD); 
   motor3.run(FORWARD); 
   motor4.run(BACKWARD);
  } 
  else if (data=='2') {
   Serial.println ("I AM MOVING IN BACKWARD DIRECTION !");
   delay (15);
   motor1.run(BACKWARD);
   motor2.run(BACKWARD); 
   motor3.run(BACKWARD); 
   motor4.run(BACKWARD); 
  } 
 
else if (data=='5') {
   Serial.println ("STOPPED");
   delay (15);
   motor3.run(RELEASE);
    motor4.run(RELEASE);
   motor2.run(RELEASE); 
   motor1.run(RELEASE); 
  }  //RELEASE IS COMMAND TO STOP MOTOR
}
}