// Importing the DHT Library of Adafruit
#include "DHT.h"

// ‘#define’ is a preprocessor directive and is a useful C++ component that allows the programmer to give a name to a constant value before the program is compiled. The compiler will replace references to these constants with the defined value at compile time and they don’t take up any program memory on the chip, unlike constants defined through variables (ie. const int variable_name = value)
#define DHTPIN 9  // Defines the Digital pin that the DHT Sensor Data Pin is connected to. Here, it is connected to GPIO9, which is the Digital Pin D9. So, all instances of ‘DHTPIN’ are replaced by the value 9. If it doesn't work on D9, please try other GPIO Pins also

#define DHTTYPE DHT22 // Defines DHT22 as the type of the DHT Sensor you are using and replaces all instances of ‘DHTTYPE’ with DHT22
// #define DHTTYPE DHT11 // Defines DHT11 as the type of the DHT Sensor you are using and replaces all instances of ‘DHTTYPE’ with DHT11.If you are using a DHT11 Sensor, uncomment this line and replace this with the above line.

DHT dht(DHTPIN, DHTTYPE);  // Creates a DHT Object using the defined DHTPIN and DHTTYPE

void setup()
{
// Initialize the Serial Monitor Baud Rate as 9600 (you can also set it to 115200 if you need more number of serial printings per second)
Serial.begin(9600);

// Initializing the DHT sensor
dht.begin(); // Initializing the defined DHT Object. This function is executed when the GLYPH C3 starts
}

void loop() 
{
// Wait a few seconds between measurements  
delay(2000);

// Reading temperature or humidity with DHT11 takes about 250 milliseconds.
// Sensor readings may also be up to 2 seconds 'old', as DHT11 has a slow Sampling Rate

float h = dht.readHumidity();  // Calling the function readHumidity() via the created DHT Object to read the Relative Humidity. This function returns a float value that represents the Relative Humidity as a percentage.

// Read the Temperature as Celsius (the default)
float t = dht.readTemperature();
  
//The function readTemperature() reads the Temperature and returns temperature in Celsius by default, but the parameter ‘true’ is passed as an argument to get the corresponding temperature in Fahrenheit also.
float f = dht.readTemperature(true);

  // The function isnan(x) is used to check if the value obtained from the DHT11 sensor is a NaN (Not a Number) value or not. The NaN values are used to identify undefined or non-representable values for floating-point elements, such as the square root of negative numbers or the result of 0/0.
  // The parameter x for this function is always a floating-point value. isnan(x) returns a non-zero value (true) if x is a NaN value; and zero (false) otherwise. If the DHT11 sensor gives a NaN value, it can cause your code to malfunction.So, the condition if (isnan(h) || isnan(t) || isnan(f)) checks if any of the h, t or f values are a NaN(Meaning any of the reads Failed), then quickly exit and try the reads again.
  if (isnan(h) || isnan(t) || isnan(f))
  {
   // F() is a macro that instructs the compiler to store the String that is passed as a parameter to the GLYPH C3’s Flash Memory, instead of the SRAM.This is a method for minimizing the amount of RAM that a sketch needs.Remember that GLYPH C3 has a Flash Memory of 4 MB, but only 320 KB of SRAM. 
   Serial.println(F("Failed to read from DHT sensor!"));  // Printing that the read Failed to the Serial Monitor

   return;  // return statement is used to exit the loop() function and return back to the hidden main() function that called it. The main() function then calls loop() again- so round and round it goes.
  }

// Computes the Heat Index in Fahrenheit (the default)
float hif = dht.computeHeatIndex(f, h);
// Computes Heat Index in Celsius by passing the parameter ‘false’ as an argument
float hic = dht.computeHeatIndex(t, h, false);

// Printing the Humidity, Temperature and Heat Index values onto the Serial Monitor
Serial.print(F("Humidity: "));
Serial.print(h);
Serial.print(F("%  Temperature: "));
Serial.print(t);
Serial.print(F("°C "));
Serial.print(f);
Serial.print(F("°F  Heat index: "));
Serial.print(hic);
Serial.print(F("°C "));
Serial.print(hif);
Serial.println(F("°F"));
}