As myself, you might be super familiar with the increment/decrement operator e.g.

++$i 
# vs
$i++

What was new to me, was that you can pre or post incrememnt, depending how you need it to behave!

Now, what’s the difference?

$i = 0

do{
    $i
}
while(
    $i++ -le 5
)

# Output:
0123456
$i = 0

do{
    $i
}
while(
    ++$i -le 5
)

# Output:
012345

It basically dictates the behaviour of when the actual incementation is happening, BEFORE (pre-increment) the eval or AFTER (post-increment)

Reference