Expected unqualified-id before if c a dire quoi?

#include <SoftwareSerial.h>
SoftwareSerial BT(9,10); // TX,RX respectively
String device;
char c;
void setup() {
BT.begin(9600);
Serial.begin(9600);
pinMode(6,OUTPUT);

}

void loop() {
while( BT.available() )
delay(10);
c = BT.read();
device += c;
}
if(device.length() > 0){
Serial.println(device);
if(device == "a")
{
digitalWrite(6,HIGH);
}
else if (device == "b")
{
digitalWrite(6,LOW);

}
device="";
}
}