PHP in a Nutshell

Incrementing and Decrementing Operators

The next two operators do different things, depending on where you place them. The difference is explained in Table 6-6.

Table 6-6. The incrementing and decrementing operators

++$a	Pre-increment	Increments $a by one, then returns $a
$a++	Post-increment	Returns $a, then increments $a by one
—$a	Pre-decrement	Decrements $a by one, then returns $a
$a—	Post-decrement	Returns $a, then decrements $a by one

The incrementing and decrementing operators can be placed either before or after a variable, and the effect is different depending on where the operator is placed. Here's a code example:

    $foo = 5;
    $bar = $foo++;
    print "Foo is $foo\n";
    print "Bar is $bar\n";

That will output the following:

    Foo is 6
    Bar is 5

The reason behind this is that ++, when placed after a variable, is the post-increment operator, which immediately returns the original value of the variable before incrementing it. In line 2 of our script, the value of $foo (5) is returned and stored in $bar, then $foo is incremented by one. If we had put the ++ before $foo rather than after it, $foo would have been incremented then returned, which would have made both $foo and $bar 6.