Got NaN answer from DHT22 - arduino

Question

I am trying to read temperature and humidity from a DHT22, here is the code:
#include "fsm_config.h"
#include <ESP8266WiFi.h>
#include <PubSubClient.h>
#include <DHT.h>
#define DHTPIN D4 // what pin we're connected to
#define DHTTYPE DHT22 // DHT 22 (AM2302)
DHT dht(DHTPIN, DHTTYPE); //// Initialize DHT sensor for normal 16mhz Arduino
const int buttonPin = D5; // definicao do pino utilizado pelo botao
const int ledPin = D7; // definicao do pino utilizado pelo led
const char* ssid = "augusto-Aspire-E5-571"; // id da rede
const char* password = "sLPCwZqX"; // senha da rede
const char* mqtt_server = "things.ubidots.com"; // server
int buttonState = LOW; // armazena a leitura atual do botao
int lastButtonState = LOW; // armazena a leitura anterior do botao
unsigned long lastDebounceTime = 0; // armazena a ultima vez que a leitura da entrada variou
unsigned long debounceDelay = 50; // tempo utilizado para implementar o debounce
float umidade; //Stores humidity value
float temperatura; //Stores temperature value
String hum = "{\"value\":";
String temp = "{\"value\":";
char humChar[50];
char tempChar[50];
WiFiClient espClient;
PubSubClient client(espClient);
int lastMsg = 1000;
int now;
char msg[60];
char msg1[60];
int send_data() {
dht.begin();
umidade = dht.readHumidity();
temperatura = dht.readTemperature();
//Print temp and humidity values to serial monitor
Serial.print("Humidity: ");
Serial.print(umidade);
Serial.print(" %, Temp: ");
Serial.print(temperatura);
Serial.println(" Celsius");
temp.concat(temperatura);
temp.concat("}");
hum.concat(umidade);
hum.concat("}");
temp.toCharArray(tempChar, 50);
hum.toCharArray(humChar, 50);
String hum = "{\"value\":";
String temp = "{\"value\":";
client.publish("/v1.6/devices/wemos/umidade", humChar);
client.publish("/v1.6/devices/wemos/temp", humChar);
delay(10000); //Delay 2 sec.
return true;
}
But I only got "NaN" as answer, what should happened? I've looked for some other questions here but none was useful for me.
Here the link for the image of the connections:

Answer 1

NaN stands for "Not a Number". Sometimes the sensor fails to read and gives you a nan value. You can't do anything against it, but in the DHT.h library is a function called isnan(). So you can make a backup variable were you store the last value that was correct. Then you can check if your sensor reads nan and if he does you can print out the backup variable:
float temperature;
float bTemperature;
temperature = dht.readTemperature();
if(!isnan(temperature)){
bTemperature = temperature;
Serial.println(temperature);
}
else{
Serial.println(bTemperature);
}