error: invalid conversion from 'int' to 'const char*' [-fpermissive]

Using Arduino Programming Questions
1

Hello, I am very new to arduino :stuck_out_tongue:
But i have an error:

bluetooth.ino: In function 'void readdata(const String&)':
bluetooth.ino:37:18: error: invalid conversion from 'int' to 'const char*' [-fpermissive]

This is my script:

#include <SoftwareSerial.h>
SoftwareSerial BT(10, 11);

String Data = "";
String str;
char character;

void setup() {
  Serial.begin(9600);
  BT.begin(9600);
  pinMode(13, OUTPUT);
}

void loop() {

  if (Serial.available() > 0){
   str = Serial.readStringUntil('/n');
   Serial.println(str);
   BT.println(str);
  }
  
  if(BT.available()){
   character = BT.read();
  Data.concat(character);
 if(character == '\n'){
   digitalWrite(13, HIGH);
  Serial.println(Data);
  readdata(Data);
  Data = "";
  delay(10);
  digitalWrite(13, LOW);
  } 
  }
}

void readdata(const String& Datastr) {
  if (Datastr == 'hoi'){
    digitalWrite(13, HIGH);
    delay(200);
    digitalWrite(13, LOW);
  }
}

I didn't had this error before adding the readdata void.
I have no idea what is wrong, can someone help me?

2 
 'hoi'

A three letter character constant?

(And they're called "functions", not "voids")

3

Ooooh now i see :blush:
Thank you for helping me.

4 
   str = Serial.readStringUntil('/n');

/n is NOT the same as \n. You will NEVER find a /n as a SINGLE character in the input stream.