For an electronic device to ‘know’ what to do, computer programmers need to give it a set of instructions, called code. Writing software programmes can be an immense task — the average Android phone uses 12 million lines of code, Facebook runs on 62 million, and a modern car on 100 million.
Because of the sheer size of code involved, starting from scratch every time you need to write a new programme would be a nightmare. Plus many software utilise similar functions, such as password authentication, copy and paste tools, or parsing a text file. So instead, some software developers employ a neat trick: code reuse, where they take existing code and use it to build new software.