An Ordinary Car

#include <AFMotor.h>
#include <SoftwareSerial.h> 
int speed_min = 0; 
int speed_max = 255;
char bt = 0; 
AF_DCMotor m1(1);

void setup() {
  Serial.begin(9600); 
}
void loop()
 {
   if (Serial.available() > 0) //save incoming data to variable 'bt'
   {
     bt = Serial.read();
     
     int x=0;
     m1.setSpeed(x);
     
if(bt == 'F')  //move forwards
     {
      int x=255;
      m1.setSpeed(x);   
      m1.run(FORWARD);
      }    
else if(bt == 'B')  //move backwards
     {
      int x=255;
      m1.setSpeed(x);
      m1.run(BACKWARD);     
      }
else
     {
      m1.setSpeed(0);  //stop
      m1.run(RELEASE);
     }
     }
     }