How to react that one of the friends of a user has logged out or logged into VK?

Question

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How to react that one of the friends of a user has logged out or logged into VK?

For example:

The program constantly goes through the friends of a particular user. If the user was online online: 1 , and left VK, thereby online: 0 , then output to the console:
- User such and such logged out from VK

Or if the user was offline online: 0 , and then went to VK online: 1 , then output to the console:
- User such and such logged into VK

Answer 1

Well, everything is as you described only in any programming language that you know

Answer 2

Is there a program code?
All this is quite possible to do with just one api vk.
Use the VK API:
vk.com/dev/friends
Using friends.get, you can get a list of the user's friends. (their id).
Create a timer for 5-10-15-20-30-60 seconds that will check the previously received id, and then:

The program constantly goes through the friends of a particular user. If the user was online online: 1, and left VK, thereby online: 0, then output to the console:
- User such and such logged out from VK
Or if the user was offline online: 0, and then went to VK online: 1, then output to the console:
- User such and such logged into VK