Connected Temperature & Humidity Sensor

#include <ESP8266WiFi.h>
#include <PubSubClient.h>
#include <DHT.h>
#include "SSD1306.h" // alias for `#include "SSD1306Wire.h"`
#define DHTPIN D4     // what pin the DHT is connected to

// Initialize the OLED display using Wire library
SSD1306  display(0x3C, D3, D5); // (I2C Address, SCL Pin, SDA Pin)

#define DHTTYPE DHT22   // DHT 22  (AM2302)
const int TEMPERATURE_INTERVAL = 30;
unsigned long last_temperature_sent = 0;

// WiFi Connection Details
const char* ssid = "Your SSID";
const char* password = "Your password";

// Raspberry Pi IP address, so it connects to your MQTT broker
const char* mqtt_server = "IP address of mqtt server";

// Change these to suit
WiFiClient wemos_lounge;
PubSubClient client(wemos_lounge);

const int HUMIDITY_INTERVAL = 30;
unsigned long last_humidity_sent = 0;
String display_temp;
String display_humid;

DHT dht(DHTPIN, DHTTYPE);

// This functions connects your ESP8266 to your router
void setup_wifi() {
  delay(10);
  // We start by connecting to a WiFi network
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(ssid);
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("");
  Serial.print("WiFi connected - ESP IP address: ");
  Serial.println(WiFi.localIP());
}

// This functions reconnects your ESP8266 to your MQTT broker
void reconnect() {
  // Loop until we're reconnected
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    if (client.connect("wemos_lounge")) {
      Serial.println("connected");  
      // Subscribe or resubscribe to a topic
      client.subscribe("heating/temperature_lounge");
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      // Wait 5 seconds before retrying
      delay(5000);
    }
  }
}
void setupHandler() {
  // Do what you want to prepare your sensor
  display.clear();
}
void getSendTemperature() {
  if (millis() - last_temperature_sent >= TEMPERATURE_INTERVAL * 1000UL || last_temperature_sent == 0) {
    float temperature = dht.readTemperature(false);
    if (isnan(temperature)) {
      Serial.println("Failed to read from DHT sensor!");
      return;
    }
// May need to offset temperature reading:
// I found the reading to be 3.1° too high
    display_temp = (temperature-3.1);
    int temp = round(temperature-3.1);
    char cstr[16];
    itoa(temp, cstr, 10);
    client.publish("heating/temperature_lounge",cstr);
    Serial.print("Temperature: ");
    Serial.print(temperature);

    Serial.println(" °C");
  }
}
void getSendHumid() {
  if (millis() - last_humidity_sent >= HUMIDITY_INTERVAL * 1000UL || last_humidity_sent == 0) {
    float humidity = dht.readHumidity();

    if (isnan(humidity)) {
      Serial.println("Failed to read from DHT sensor!");
      return;
    }
    display_humid = humidity;
    int humid = round(humidity);
    char cstr[16];
    itoa(humid, cstr, 10);
    client.publish("heating/humidity_lounge", cstr);
    Serial.print("Humidity: ");
    Serial.print(humidity);
    Serial.println(" %");
  }
 }
void displayData() {
    display.clear();
    display.setTextAlignment(TEXT_ALIGN_CENTER);
    display.setFont(ArialMT_Plain_24);
    display.drawString(66, 5, display_temp + "C");
    display.drawString(66, 35, display_humid + "%");
    display.display();
}
void setup() {

  Serial.begin(115200);
  setup_wifi();
  client.setServer(mqtt_server, 1883);
  // Initialising the display.
  WiFi.mode(WIFI_STA);
  display.init();
  display.clear();
  display.flipScreenVertically();
  display.setTextAlignment(TEXT_ALIGN_CENTER);
  display.display();
}
void loop() {
  //connect wifi if not connected
  if (WiFi.status() != WL_CONNECTED) {
    delay(1);
    setup_wifi();
    return;
}
  if (!client.connected()) {
    reconnect();
  }
  if(!client.loop())
    client.connect("wemos_lounge");
  getSendTemperature();
  getSendHumid(); 
  displayData();
  delay(2000);
}