serial is print twice? I have a problem , when send 1 or 0 by Bluetooth module the serial monitor print two time (RECEIVED SMS) . what's the wrong ?

This is my code  :

   char BluetoothData = 0 ; 
void setup() {
  // initialize serial communication:
  Serial.begin(9600);
    for (int pin = 1; pin &lt;= 13; pin++)
     {
       pinMode(pin, OUTPUT); // sets the digitals pin  as outputs
       digitalWrite(pin, LOW); // sets the digitals pin off defult intial states 
     }  
       Serial.println("ALL LEDs NOW OFF \n "); 
       Serial.println("Please, Enter : ( 1 to Turn on All LEDs )  or ( 0 to Turn off LEDs ) \n");
}
void loop() {            
  // read the sensor:
  if (Serial.available() &gt; 0) {

        BluetoothData = Serial.read();
            Serial.print("*** RECEIVED SMS *** : ==&gt;&gt; ");
            Serial.println(BluetoothData);

        if (BluetoothData == '1'){ 
        for (int Pin = 1; Pin &lt;= 13; Pin++) {
          digitalWrite(Pin, HIGH);
          }  
          Serial.println("ALL LEDs NOW ON");
         }
        // turn all the LEDs off:
   else if (BluetoothData == '0') {
        for (int Pin = 1; Pin &lt;= 13; Pin++) {
          digitalWrite(Pin, LOW);
          }
          Serial.println("ALL LEDs NOW OFF"); 
         }
  }
   delay(100);  
} 


This is photo for serial monitor
Probably the first time because you received the character '1' or '0'.
The second character is probably a '\0' or '\d', an end-of-string or end-of-line character.

You can easily check this by printing the value of each received character, like 

Serial.println((int)(BluetoothData));


You probably see the value for '0' (48), '1' (49), end of string '0' of end of line '13' or maybe '10' (new line).