There are a lot of opinions about coding conventions. If you ask 10 people what it is about, you will get 11 opinions.
The style you cite with a 1/2/3 letter lowercase prefix is called "Hungarian notation" (ask Google) and was most popular with Microsoft code in the early years. It has fallen out of favor for the most part, especially when prefixes can't easily be found for class or struct instances.
A book I like on coding conventions is C++ Coding Standards
], by Herb Sutter and Andrei Alexandrescu (who are opposed to Hungarian notation).
Regardless, I still use some of the features of Hungarian, such as "m_" prefix for member variables and several other artifacts. I find it makes the code easier to develop and maintain.