One of the most basic building blocks of programming are functions. You can write extremely simple programs without them, but everything beyond “Hello World” demos will likely need to utilize functions eventually.
Have you ever wondered why functions are a cornerstone of so many programming languages? Let’s look into the reasons why they’re so vital and what they do for programmers.
What Is a Function, Anyway?
Simply put, a function in programming is a named group of code that performs a specific task. Depending on the language, you may also hear them called subroutines or procedures.
Once you define a function, you put code in it just like you would anywhere else in the program. By giving the function a name and defining parameters it should accept, you can pass information to the function and return some result. Functions are re-usable, so once you write one, you can call it anywhere else in your program.
So functions are useful, but what purposes do they serve?
1. Functions Encapsulate Tasks
Introductory programming classes often describe functions as “black boxes.” That is, when a programmer calls a function, they don’t care what exactly the code inside it does; they just need the result.
For example, if you wrote a function to read in lots of numbers from a text file and calculate the mode, you wouldn’t need to know how it works to use it. As long as you knew that the function expects a text file filled with numbers as input and outputs a number as the result, you could use it in any program without much trouble.
2. Functions Separate Tasks
But this isn’t the only way that functions encapsulate code. They also allow programmers to cleanly divide their code into segments.
While your main function might only have a few dozen lines of code, it could call multiple functions and perform complex operations through them. This is the core of object-oriented programming. Plus, it helps split up large programs into smaller pieces so multiple people can work on them.
3. Functions Let You Reuse Code
Chances are that when you write some code to perform a task, you’ll use it more than once in your program.
Copying and pasting the needed code into multiple places is a bad idea. Not only does it add more complexity to your program, but it introduces more places for something to go wrong. If you change something in the original block, you have to remember to re-paste it everywhere else.
Functions eliminate this problem. They make it easy to reuse code anywhere else in your program. Once you’ve defined a function, you can call it anytime and be sure that it will run the same way. This saves time and reduces complexity, which are two welcome qualities for a program.
4. Functions Enable Easier Shareability
At many companies today, the functions one programmer writes may be used by others in the company in other projects.
Since functions stand on their own, they’re very portable. Reusing them where appropriate cuts down on duplicate work, makes more efficient use of programming resources, and helps with developing standards across a company.
5. Functions Make Testing and Debugging Easier
Most programmers know the pain of trying to debug spaghetti code: a tangled, confusing mess that’s nearly impossible to follow as it has little structure. Without clear functions, programs jump all over the place. This makes it hard to debug, and a massive pain for someone coming in fresh to understand.
With everything clearly divided into functions, programmers can use unit tests to confirm that these functions work as they should. Instead of having to sort through the entire program to pinpoint an issue, they can isolate it to one function.
Functions increase readability, as well. A clean set of code goes a long way in making it easy to maintain and follow. One alternative is confusing GOTO statements, which are heavily discouraged in modern programming.
Consider the simple example from Wikipedia, first with GOTO statements and then with a structured style, to see how this makes a difference:
1 i=0 2 i+=1 3 PRINT i; "squared=";i*i 4 IF i>100 THEN GOTO 6 5 GOTO 2 6 PRINT "Program Completed." 7 END 1 FOR i=1 TO 100 2 PRINT i;"squared=";i*i 3 NEXT i 4 PRINT "Program Completed." 5 END
6. Functions Divide Data and Logic
We talked about abstraction above; it’s important to note that functions help you separate the steps from the actual data. As long as you pass the function parameters it’s expecting, it doesn’t care what the data is. Each run of that function creates temporary variables and then discards them after it returns a result. This keeps your namespace clear and lets you reuse short-term variable names like “x”.
Keeping your important data outside the functions helps prevent unwanted modification. This is a smart step in modern programming.
7. Built-In Functions Are Important Too
Typically when we discuss functions we’re talking about user-created functions, but they aren’t the only type of function. All programming languages include functions that you can use without having to create them yourself.
For instance, no matter which language you’re using, you don’t have to write functions for basic arithmetic, printing text to the screen, and similar tasks. Can you imagine what a waste of time it would be if you were required to tell the computer how to perform these basic operations?
Functions Are Vital for Programming
Now you know why programming languages use functions, and why they’re so important. The biggest reasons for including functions all come down to one truth: functions allow you to break a program into more manageable pieces. When you do this, your program becomes simpler to manage, easier to test, and apt for reuse.
Without functions, programs would have loads of duplicate code, wouldn’t flow in a logical order, and would have no separation of utility. That would be a nightmare for managing, testing, and debugging. Thank goodness programming languages use them!
For more programming basics, check out our explanation on how do-while loops work.