A Speed driver ussing PWM and a Arduino

pwm_motor.cpp

int pin = 11;
int val = 255;
int command;

void printMsg(){
  Serial.println("Welcome to speed controller");
  Serial.println(" type  ");
  Serial.println(" - z : to speed up "); 
  Serial.println(" - x : to speed down"); 
  Serial.println(" - s : set manually(submenu)"); 
}

void setup(){
  Serial.begin(9600);
  pinMode(pin, OUTPUT);
  printMsg();
}


void loop(){
  analogWrite(pin,val);
  if(Serial.available()>0){
    command = Serial.read();
    if(command == int('z')){
      val = val +1;
      Serial.println("+  speed \n ->");
      Serial.print(val*100/255);
      Serial.println("% ");
    }else if(command == int('x')){
      val = val -1;
      Serial.println("- speed");
      Serial.print(val*100/255);
      Serial.println("% ");
    }else if(command == int('s')){
      Serial.println("o : off");
      Serial.println("f : full on");
      while(Serial.available()>0){
        analogWrite(pin,val);
        command = Serial.read();
        if(command == int('o')){
          val = 0;
          Serial.println(" -> speed: 0%");
        }else if(command == int('f')){
          val = 255;
          Serial.println(" -> speed: 100%");
        }else{
          Serial.println("Unknow command");
          continue;
        }        
      }
      
    }else{
      Serial.println("unknow command:"+command);
    }
  }
  
}