Based on a development environment instance C++ Circle, that is known radius of the ring, seeking the ring area

CircleExample
.............\CircleExample
.............\.............\CircleExample.vcxproj
.............\.............\CircleExample.vcxproj.filters
.............\.............\CircleExample.vcxproj.user
.............\.............\Debug
.............\.............\.....\CL.read.1.tlog
.............\.............\.....\CL.write.1.tlog
.............\.............\.....\CircleExample.exe.intermediate.manifest
.............\.............\.....\CircleExample.lastbuildstate
.............\.............\.....\CircleExample.log
.............\.............\.....\CircleExample.vcxprojResolveAssemblyReference.cache
.............\.............\.....\CircleExample.write.1.tlog
.............\.............\.....\Main.obj
.............\.............\.....\link.read.1.tlog
.............\.............\.....\link.write.1.tlog
.............\.............\.....\mt.read.1.tlog
.............\.............\.....\mt.write.1.tlog
.............\.............\.....\vc100.idb
.............\.............\.....\vc100.pdb
.............\.............\Main.cpp
.............\CircleExample.sdf
.............\CircleExample.sln
.............\CircleExample.suo
.............\Debug
.............\.....\CircleExample.exe
.............\.....\CircleExample.ilk
.............\.....\CircleExample.pdb
.............\ipch
.............\....\circleexample-63404da9
.............\....\......................\circleexample-a5cb6cca.ipch

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