PHP: Increment and decrement
Two operations are carried over from C to PHP: Increment ++ and Decrement --, which are very common with loops. These unary operations increment and decrement by one the number written in the variable.
<?php
$i = 0;
$i++; // 0
$i++; // 1
$i--; // 2
$i--; // 1
When using a prefix, it's the other way around: first you change the variable and then return the new value:
<?php
$i = 0;
++$i; // 1
++$i; // 2
--$i; // 1
--$i; // 0
It seems there's no difference between using prefix and postfix notation. But this is where it gets complicated.
Unlike other operators, which have no side-effects and simply return a new value, increment and decrement not only return a value but also change it.
If you use prefix notation, the variable is changed first, and then it's returned.
When using postfix notation, it's the other way around: first it's returned and then the variable is changed.
The rule works exactly the same for both incrementing and decrementing. For simplicity's sake, we'll only look at increments for now:
<?php
$x = 5;
echo ++$x; // => 6
echo $x; // => 6
echo $x++; // => 6
echo $x; // => 7
What's going on?
- We've printed
++$x. It's a prefix increment, so first the value is increased by 1, and then the result is returned and printed. - Since the value has changed,
echo $xoutputs 6. - Now display
$x++. This is a postfix increment, so first the value was returned and displayed, and then the variable was incremented by 1. - Since the value has changed,
echo $xoutputs 7.
Increment and decrement can make code very complex. Things get especially scary when increments are inserted inside other operations: $x = $i++ - 7 + --$h. It's impossible to understand such code, and writing it should be considered a serious crime.
For example, in JavaScript, the linter (the program that checks the code) immediately starts to complain when it sees increment and decrement being used.
Usage guidelines:
- Never mix operations/functions that don't have side effects with operations/functions that do have side effects within a single expression.
- Use increment and decrement only if there's no difference between the prefix and postfix version. It should be separate from other expressions and on a separate line of code.
Instructions
Increment and decrement are not very important operations in PHP, and you can easily manage without them. The assignment in this lesson is not directly related to this topic, but you can use increment and decrement to get used to them. Otherwise, this exercise is just more practice with loops, strings, and conditions.
Write a function, makeItFunny(), which returns a copy of a string passed to it, where each nth element is uppercase. n also needs to be passed to the function.
To find each nth element, you will need to find the remainder from division %. Think about how you can use it.
<?php
$text = 'I never look back';
// Every third element
makeItFunny($text, 3); // 'I NevEr LooK bAck'
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.
languages.lessons.show.chat.guest
Your exercise will be checked with these tests:
1<?php
2
3namespace HexletBasics\Loops\Mutators;
4
5use PHPUnit\Framework\TestCase;
6
7class SolutionTest extends TestCase
8{
9 public function test()
10 {
11 require 'index.php';
12 $text = 'I never look back';
13 $this->assertEquals('I NevEr LooK bAck', makeItFunny($text, 3));
14 $this->assertEquals('hElLo', makeItFunny('hello', 2));
15 }
16}
17Teacher's solution will be available in:
