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?

1. 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.
2. Since the value has changed, echo $x outputs 6.
3. Now display $x++. This is a postfix increment, so first the value was returned and displayed, and then the variable was incremented by 1.
4. Since the value has changed, echo $x outputs 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'