Small post to note down a small thing about programming that I learnt today because of some error I was getting.
I will speak for C++ here.
So, basically, you would have divided your code in header files (.h) and the source files (.cpp). Now to refer to these files you will do an #include “somefile.h”
The error you might potentially run into is that of duplicate declarations. How?
Now when we do the expansion of the #include, it is clear to see that we will have multiple declarations of the variable A which will lead to a compilation error.
Include guards are a good practice followed while programming to avoid such scenarios. Basically all you do is that ensure if a header file is already present in the file, it need not be expanded again.
So, I will change my File1.h to add include guards like follows:
Now, as will be rightly noted, a second expansion of File1.h will not allow for a duplicate declaration of variable A as #ifndef will evaluate as false.
This SO answer is better than my explanation, btw: