Arduino Bluetooth car

char t;

void setup() {
pinMode(13,OUTPUT); //left motors forward
pinMode(12,OUTPUT); //left motors reverse
pinMode(11,OUTPUT); //right motors forward
pinMode(10,OUTPUT); //right motors reverse
Serial.begin(9600);

}

void loop() {
if(Serial.available()){
t = Serial.read();
Serial.println(t);
}

if(t == 'F'){ //move forward(all motors rotate in forward direction)
digitalWrite(13,HIGH);
digitalWrite(12,LOW);
digitalWrite(11,HIGH);
digitalWrite(10,LOW);
}
else if (t =='B'){
digitalWrite(13,LOW);
digitalWrite(12,HIGH);
digitalWrite(11,LOW);
digitalWrite(10,HIGH);
}

else if(t == 'R'){ //turn right (left side motors rotate in forward direction, right side motors doesn't rotate)
digitalWrite(13,HIGH);

}

else if(t == 'L'){ //turn left (right side motors rotate in forward direction, left side motors doesn't rotate)
digitalWrite(11,HIGH);

}

else if(t == 'S'){ //STOP (all motors stop)
digitalWrite(13,LOW);
digitalWrite(12,LOW); 
digitalWrite(11,LOW);
digitalWrite(10,LOW);
}
delay(100);
}