Bluetooth controlled car

#include <AFMotor.h>//made by hirusha nirmal
AF_DCMotor R2(1);
AF_DCMotor R1(2);
AF_DCMotor L2(3);
AF_DCMotor L1 (4);

char bt='s';
void setup() {
  Serial.begin(9600);

R1.setSpeed(255);
R2.setSpeed(255);
L1.setSpeed(255);
L2.setSpeed(255);
Stop();

}

void loop() {
 bt=Serial.read();

 if (bt=='F')
 {
  forward();
 }

 if (bt=='B')
 {
  backward();
 }

 if (bt=='R')
 {
  right();
 }

 if  (bt=='L')
 {
  left();
 }

 if (bt=='S')
 {
  Stop();
 }
 }
void forward()
{
  R1.run(FORWARD);
  R2.run(FORWARD);
  L1.run(FORWARD);
  L2.run(FORWARD);
}

void backward()
{
  R1.run(BACKWARD);
  R2.run(BACKWARD);
  L1.run(BACKWARD);
  L2.run(BACKWARD); 
}

void right()
{
  R1.run(BACKWARD);
  R2.run(BACKWARD);
  L1.run(FORWARD);
  L2.run(FORWARD); 
}

 void left()
 {
  R1.run(FORWARD);
  R2.run(FORWARD);
  L1.run(BACKWARD);
  L2.run(BACKWARD); 
}

void Stop()
{
  R1.run(RELEASE);
  R2.run(RELEASE);
  L1.run(RELEASE);
  L2.run(RELEASE); 
}//made by hirusha nirmall