Savoir si son transistor est un NPN ou un PNP avec un arduino

int a=13;//pins for transistor//
int b=12;
int c=11;
String type="";

void setup(){
  Serial.begin(9600);
}
void loop(){
 
  Serial.println("Pin status");
  Serial.println("----------");
 
  //a=1
  pinMode(a,OUTPUT);
  pinMode(b,INPUT);
  pinMode(c,INPUT);
 
  digitalWrite(a,HIGH);
 
  if (digitalRead(b)==1 ||digitalRead(c)==1){
    Serial.println("Pin 13 semiconductor is positive");
    type=type+"P";
  }else{
    Serial.println("Pin 13 semiconductor is negative");
    type=type+"N";
  }
 
  digitalWrite(a,LOW);
 
  //b=1
 
  pinMode(a,INPUT);
  pinMode(b,OUTPUT);
  pinMode(c,INPUT);
 
  digitalWrite(b,HIGH);
  
  if (digitalRead(a)==1 ||digitalRead(c)==1){
    Serial.println("Pin 12 semiconductor is positive");
    type=type+"P";
  }else{
    Serial.println("Pin 12 semiconductor is negative");
    type=type+"N";
  }
 
  digitalWrite(b,LOW);
 
  //c=1
  pinMode(a,INPUT);
  pinMode(b,INPUT);
  pinMode(c,OUTPUT);
 
  digitalWrite(c,HIGH);
 
  if (digitalRead(a)==1 ||digitalRead(b)==1){
    Serial.println("Pin 11 semiconductor is positive");
    type=type+"P";
  }else{
    Serial.println("Pin 11 semiconductor is negative");
    type=type+"N";
  }
 
  digitalWrite(c,LOW);
 
  Serial.println("-------");
  Serial.println("Result");
  Serial.println("-------");
 
  if(type=="NPN" || type=="NNP" || type=="PNN"){
    Serial.println("This transistor is NPN type transistor");
  }
    if(type=="PNP" || type=="NPP" || type=="PPN"){
    Serial.println("This transistor is PNP type transistor");
  }
  if (type=="NNN"){
    Serial.println("Please attach your transistor");
  }
  if (type=="PPP"){
    Serial.println("Burnt transistors or not connected properly");
  }
 
  Serial.println("-----------------------------");
  Serial.println("");
  Serial.println("");
 
  type="";
 
  delay(2000);



}