Thanks to all of you who tried to help. As far as I can see, I have all my components in the directories you nominated, but still, nothing happens when I click on Build & Run, and there is no executable created - in Linux, that is. However, CODE::BLOCKS downloaded and installed into Windows 10 does work! While Windows displeases me in so many ways, I have to admit that it is so much easier to install applications under Windows than it is under Linux. So, for the time being, I will use the Windows version of CODE::BLOCKS to teach myself C++ and when I have time I will revise my knowledge of Linux (I graduated from university with an IT degree in 2003, so I have forgotten a lot of what I learned about Linux). Then I might be able to understand your advice. What is quite clear and logical to you competent Linux users is just gobbly-gook to those of us who do not know Linux, or have not used it for a decade or more and forgotten most of what we once knew. When I have re-learned Linux, I will re-read your advices and try and sort out my copy of CODE::BLOCKS, and, hopefully, get away from using Windows.
Many thanks, James.