Unfortunately, obtaining the source code used to produce a C++ executable from only the executable itself is an unsolved problem and reverse engineering is a generally difficult and labour-intensive process. However, there are tools that will help to reduce the level of pain involved.
The Hex-Rays Decompiler for IDA Pro will produce a remarkably good result in functional terms, but its output won't closely resemble the code you remember writing.
Ghidra looks like a good open-source alternative, though I haven't tried it myself.
The hosts - Carl and Richard - do a brilliant job of keeping their shows entertaining and informative.