was not declared in this scope

I have a problem with my code this is the error message:

exit status 1

‘esp8266’ was not declared in this scope

ESP8266_MQ135_MQ7_DHT11.ino (3.76 KB)

why not use "Serial.println()"?

More members will see your code if posted properly. Read the how get the most out of this forum sticky to see how to properly post code. Remove useless white space and format the code with the IDE autoformat tool (crtl-t or Tools, Auto Format) before posting code.

Please include the entire error message. It is easy to do. There is a button (lower right of the IDE window) called "copy error message". Copy the error and paste into a post in code tags. Paraphrasing the error message leaves out important information.

You include the SoftwareSerial library, but do not construct an instance or initialize it.

SoftwareSerial esp8266(RX, TX);
// and in setup()
esp8266.begin(baud); // insert your baud rate