I have a piece of code I keep using in new notebooks over and over again and I have to copy and paste it in each new notebook. Problem arises: if I update the code in one file I have to manually do it in all the other files. So I was wondering, is it possible to create one file, let's call it InitCode-7 July.nb, and use a command as an initialization cell in Mathematica to load it? This way I would only have one file to change and it would apply to all the files where I use the same code.
I am familiar with the concept of headers file in other programming languages but I have no idea how to do it in Mathematica. Thank you.