Trying to use a relais with a DS18S20 Temp.-sensor

Using Arduino Sensors
1

Hi!
My problem is a giant gap to me, maybe a tiny step for others:

What is the variable I can use to tell the program it shall activate a relais after its value is smaller then a given value of the DS18S20?

Not to bore you, but to demonstrate what I mean I sent the code I tried to use below.
In front of the if-loop I mentioned my problem after the double-slash again.
As well I don't know if my if-loop is at the best place. If not: Could someone tell me why?

#include <Wire.h>

#include <OneWire.h>

#include <DallasTemperature.h>

#define ONE_WIRE_BUS 2  //Sensor DS18B20 am digitalen Pin 2
#define DS18S20_ID 0x10 // No idea what that means ...

  printValue(sensors.getTempCByIndex(i), "°C");
  printValue(sensors.getTempFByIndex(i), "°F");
sensors.requestTemperatures();

// Here is my problem: What can I use to tell the programm I want it to compare
// the measured temperature with the given value???
Until now no one could tell me ... I hope someone here can.

if(THE NEEDED VARIABLE OR SOMETHING > 17){
 digitalWrite(relaisPin, LOW);
} else{
 digitalWrite(relaisPin, HIGH);
} 


 }
 
 delay(1000); //Pause von 1 Sekunde.
} 
 
void printValue(float value, String text){
  Serial.print("\t\t");
  Serial.print(value);
  Serial.println(text);
  

}
2

You need to start at the beginning, and work through the simple examples that come with Arduino. Blink an LED, read a voltage, a switch or a sensor, send data to the serial monitor, etc. Look for on-line tutorials, too.

That way you learn the language and the special features of the Arduino, and avoid the sort of frustration you are now having.