Arduino bluetooth car

char a;

#define m1 7  
#define m2 6  
#define m3 5  
#define m4 4  


#define fl 8   //front lights
#define fl2 9

#define bl 10//back lights
#define bl2 11
void setup() {
  pinMode(m1, OUTPUT);
  pinMode(m2, OUTPUT);
  pinMode(m3, OUTPUT); 
  pinMode(m4, OUTPUT);   
  pinMode(fl, OUTPUT); 
  pinMode(fl2, OUTPUT); 
  pinMode(bl, OUTPUT); 
  pinMode(bl2, OUTPUT); 
Serial.begin(9600);
 
}
 
void loop() {
if(Serial.available()){
  a = Serial.read();
  Serial.println(a);
}
 
if(a == 'F'){            
  digitalWrite(m1, HIGH);
  digitalWrite(m2, LOW);
  digitalWrite(m3, HIGH);
  digitalWrite(m4, LOW);
}
 
else if(a == 'B'){      
  digitalWrite(m2, HIGH);
  digitalWrite(m1, LOW);
  digitalWrite(m4, HIGH);
  digitalWrite(m3, LOW);
}
 
else if(a == 'L'){     
  digitalWrite(m1, LOW);
  digitalWrite(m2, LOW);
  digitalWrite(m3, HIGH);
  digitalWrite(m4, LOW);
}
 
else if(a == 'R'){      
  digitalWrite(m1, HIGH);
  digitalWrite(m2, LOW);
  digitalWrite(m3, LOW);
  digitalWrite(m4, LOW);
}
else if(a == 'W'){     
  digitalWrite(fl, HIGH);
  digitalWrite(fl2, HIGH);
}
else if(a == 'w'){      
  digitalWrite(fl, LOW);
  digitalWrite(fl2, LOW);
}
else if(a == 'U'){      
  digitalWrite(bl, HIGH);
  digitalWrite(bl2, HIGH);
}
else if(a == 'u'){      
  digitalWrite(bl, LOW);
  digitalWrite(bl2, LOW);
}

else{     
  digitalWrite(m1,LOW);
  digitalWrite(m2,LOW);
  digitalWrite(m3,LOW);
  digitalWrite(m4,LOW);
}

delay(100);
}