I am not really going to make this system but I am taking one example for easy understanding.
In which case I will not really tell you how to do this, just offer some clues...
Suppose I want to make smart system that would be monitor...[temperature]
So just read temperatures from whatever temperature measuring devices you have in whatever programming language like to do it in. There are many such devices and many libraries in all kind of languages to help with that.
...and control temperatures
Without any idea of what you are using to raise or lower temperature it is impossible to advise. But again most any hardware can be controlled from a Pi using whatever language you like given a suitable hardware interface.
With a means of measurement and a means of control you have everything you need to set up a "smart device". That is to say a normal program that takes temperature as an input and controls your heater/cooler in order to reach some required temperature.
My research say I have to run server on raspberry pi. so that It can be control AC over web browser.
Ah, if you want to monitor what your system is doing and/or set it's parameters from a web browser you will need a web server.
But How to monitor temperature of AC?
See above. It all depends on your temperature sensor how you connect to it and read it's temperature. Cannot advise further without a specific device in mind.
I think, I have to store the temperature reading on database
Why? If you want to record a history of temperatures over time then by all means save them to a database. Not really required for basic temperature control.
I have to run one server on raspberry like apache
Memory in C++ is a leaky abstraction .