As Neil and aaronis have mentioned, you're talking about a form of Hungarian Notation. Since C++ is a strongly-typed language, it's generally considered a bad idea. It makes it harder to read the code, because there are a bunch of extra characters getting in the way.
The original Hungarian notation was actually used to signal information beyond what types told. For example, let's say I am doing some graphics work and I have points in various coordinate system. They're all of type Point, but some are in object coordinates, some are in camera coordinates, and some are in world coordinates. In that case, it makes good sense to name their respective variables something like oPt, cPt, and wPt.
Historically, this "apps" Hungarian seemed like a good idea (extra character codes to indicate non-type information) to some people and they went way too far turning it into "systems" Hungarian (extra character codes to indicate the C++ type), which is frowned upon these days.