Minimum C application for a snmp agent

I am beginning to know the net-snmp api for C applications and I have tried to find a simple example of an SNMP agent that is able to respond with GetResponse to GetRequest, GetNextRequest or SetRequest received from an NMS.
I have not found any such example, nor tutorials or books that explain it.
Is there a tutorial or an example (web, GitHub or GitLab) that serves as a starting point?

We cannot help for NET-SNMP or pure C here in this forum. But the n C++ is ok too, then you can download SNMP++ and AGENT++ from https://www.agentpp.com/download.html unpack both in the same (empty) directory on a Linux machine autoconf (see corresponding README.autoconf) and compile them with

autoreconf -i
./configure
sudo make install

In the folder

agent++/examples/atm-mib

you will find a fully functional SNMP agent examples including sources.
The tutorial that helps to understand the basics about AGENT++ can be found here - although it is about an outdated version 2, the fundamental concepts are still valid: