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PHP: Functions and how they're called

Addition, concatenation, and the other operations discussed are all fairly basic features of programming languages. Mathematics isn't limited to arithmetic, but there are many other areas with their own operations, such as geometry. The same goes for strings: you can flip them, change a letter's case, delete extra characters – and that's just the tip of the iceberg. And finally, at a higher level, there's the applied logic of a particular program. Programs withdraw money, calculate taxes, and generate reports. The number of these jobs is endless and different for each program. And they all have to be somehow expressed in code.

The notion of a function expresses any arbitrary operation in programming. Functions can be both built-in and manually written by a programmer. One built-in function we're already familiar with is print_r().

Functions are fundamental building blocks in programming, and it's impossible to accomplish anything without them. We need to get acquainted with them as soon as possible because future courses will deal almost exclusively with functions. First, we'll learn how to use the functions we've already defined, and we'll also learn to define our own functions.

We will start with basic functions that handle strings. Below is an example of a call to strrev(), that reverses a string:


// Call the strrev function with the argument 'Hello!'
$result = strrev('Hello!');
print_r($result); // => '!olleH'

We created a variable, $result and told the interpreter to write the result of the strrev() function to it. In this sense, functions are identical to operations; they always return the result of their work. The entry strrev('Hello!') means that a function named strrev is being called, to which the argument (or parameter) 'Hello!' has been passed. Arguments are needed for functions to work, just like how operators need operands. The strrev() function flips the string passed to it in the arguments.

Another example is the strlen() function, which counts the number of characters in a string


$result = strlen('Hello!');
print_r($result); // => 6

The function being called is always indicated by parentheses () following the function name. There can be any number of arguments in brackets, and sometimes none at all. The number depends on the function used, for example, the pow() function takes two arguments as input and raises the number passed to the power passed in the second parameter.


$result = pow(2, 3); // 2 * 2 * 2
print_r($result); // => 8

// Modern PHP now has a special operator for exponentiation:
$result = 2 ** 3; // 8

And here's an example of a function that takes no arguments. The rand() function generates and returns a random number:


$result = rand();

By and large, operators and functions are the same thing. The only key difference is how they're written. If you think of addition as a function, it would look like this:


3 + 5; // 8
sum(3, 5); // 8

// Or even like this
+(3, 5);

// In PHP this syntax isn't possible, but there are languages (e.g. lisp),
// where it looks very similar (take a look at the Racket course)

Self-check. How do I know what the print_r() call returns? Test it.


There are two variables defined in the program code that contain the names of companies. Calculate their total character length and print it.

The exercise doesn't pass checking. What to do? 😶

If you've reached a deadlock it's time to ask your question in the «Discussions». How ask a question correctly:

  • Be sure to attach the test output, without it it's almost impossible to figure out what went wrong, even if you show your code. It's complicated for developers to execute code in their heads, but having a mistake before their eyes most probably will be helpful.
In my environment the code works, but not here 🤨

Tests are designed so that they test the solution in different ways and against different data. Often the solution works with one kind of input data but doesn't work with others. Check the «Tests» tab to figure this out, you can find hints at the error output.

My code is different from the teacher's one 🤔

It's fine. 🙆 One task in programming can be solved in many different ways. If your code passed all tests, it complies with the task conditions.

In some rare cases, the solution may be adjusted to the tests, but this can be seen immediately.

I've read the lessons but nothing is clear 🙄

It's hard to make educational materials that will suit everyone. We do our best but there is always something to improve. If you see a material that is not clear to you, describe the problem in “Discussions”. It will be great if you'll write unclear points in the question form. Usually, we need a few days for corrections.

By the way, you can participate in courses improvement. There is a link below to the lessons course code which you can edit right in your browser.


  • A function is an operation capable of accepting data and returning a result; a function is called like this: foo().

  • An argument is the information the function receives when it is called. For example, with foo(42), we pass the argument42tofoo()`

If you got stuck and don't know what to do, you can ask a question in our community