C is a minimalist language. It gives you the bare bones of programming. You get variables, loops, and control flow. That is it. If you want to read from a keyboard or print to a screen, C doesn’t have those functions built-in. You have to write them or use a library.
This is why libraries in C are so critical. They are chunks of code that programmers extract from their projects to make them reusable. You’ve likely used the standard I/O library, or stdio, without thinking about it. But beyond that, there are libraries for math, strings, and time. You can build your own.
Splitting your code into modules makes it easier to test, debug, and understand. It also lets you reuse logic across different programs. Let’s look at how to take a monolithic script and turn a piece of it into a portable function.
Extracting Logic from a Monolith
Consider this C program. It fills an array with random numbers, sorts them using a bubble sort algorithm, and prints the results.
The sorting logic here is buried inside main. To make this reusable, we need to extract the bubble sort.
Creating a Basic Function
The array a and the constant MAX are global in this example. This means the sorting function doesn’t strictly need parameters to access them. However, good practice dictates using local variables for the loop counters (x, y, t ) to keep the function self-contained.
Here is the refactored code. We isolated the sorting logic into bubble_sort.
You pass the number of elements to bubble_sort instead of hardcoding MAX. It works. But it is still tied to the global array a.
Generalizing for True Reusability
A function is only truly reusable if it doesn’t depend on global state. We can generalize bubble_sort further by passing the array itself as a parameter.
Change the function signature to:
This tells the compiler to accept an integer array of any size. The body of bubble_sort doesn’t change. You just update the call in main :
Note that we do not use &a in the function call. You might expect to pass the address because the sort modifies the array, but in C, arrays decay to pointers when
