Expressions are the most important building blocks of PHP. In PHP, almost anything you write is an expression. The simplest yet most accurate way to define an expression is "anything that has a value".
The most basic forms of expressions are constants and variables. When you type $a = 5, you're assigning 5 into $a. 5, obviously, has the value 5, or in other words 5 is an expression with the value of
5 [in this case, 5 is an integer constant].
After this assignment, you'd expect $a's value to be 5 as well, so if you wrote $b = $a, you'd expect it to behave just as if you wrote $b = 5. In other words, $a is an expression with the value of 5 as well. If everything works right, this is exactly what will happen.
Slightly more complex examples for expressions are functions. For instance, consider the following function:
Assuming you're familiar with the concept of functions [if you're not, take a look at the chapter about functions], you'd assume that typing $c = foo[] is essentially just like writing $c = 5, and you're right. Functions are expressions with the value of their return value. Since 50 returns 5, the value of the expression '50' is 5. Usually functions don't just return a static value but
compute something.
Of course, values in PHP don't have to be integers, and very often they aren't. PHP supports four scalar value types: int values, floating point values [float], string values and bool values [scalar values are values that you can't 'break' into smaller pieces, unlike arrays, for instance]. PHP also supports two composite [non-scalar] types: arrays and objects. Each of these value types can be assigned into variables or returned from functions.
PHP takes expressions much further, in the same way many other languages do. PHP is an expression-oriented language, in the sense that almost everything is an expression. Consider the example we've already dealt with, $a = 5. It's easy to see that there are two values involved here, the value of the integer constant 5, and the value of $a which is being updated to 5 as well. But the truth is that there's one additional value involved here,
and that's the value of the assignment itself. The assignment itself evaluates to the assigned value, in this case 5. In practice, it means that $a = 5, regardless of what it does, is an expression with the value 5. Thus, writing something like 55 is like writing 56 [a semicolon marks the end of a statement]. Since assignments are parsed in a right to left order, you can also write 57.
Another good example of expression orientation is pre- and post-increment and
decrement. Users of PHP and many other languages may be familiar with the notation of 58 and 59. These are increment and decrement operators. In PHP, like in C, there are two types of increment - pre-increment and post-increment. Both pre-increment and post-increment essentially increment the variable, and the effect on the variable is identical. The difference is with the value of the
increment expression. Pre-increment, which is written 50, evaluates to the incremented value [PHP increments the variable before reading its value, thus the name 'pre-increment']. Post-increment, which is written 51 evaluates to the original value of $variable, before it was incremented [PHP increments the variable after reading its value, thus the name 'post-increment'].
A very common type of expressions are
comparison expressions. These expressions evaluate to either 52 or 53. PHP supports > [bigger than], >= [bigger than or equal to], == [equal], != [not equal], < [smaller than] and
0
1
2
3
4
5
6
7
8
$b = 50Oliver tại Hankeln-Online Dot de ¶ ¶
20 năm trước
$c = foo[]0
$c = foo[]1
$c = foo[]2
$c = foo[]3
$b = 50Chriswarbo tại Gmail Dot Com ¶ ¶
9 năm trước
$c = foo[]5
$c = foo[]6
$c = foo[]7
$c = foo[]8
$c = foo[]9
$c = 50
$c = 51
$c = 52
$b = 50Oliver tại Hankeln-Online Dot de ¶ ¶
9 năm trước
$c = 54
$c = 55
$b = 50Oliver tại Hankeln-Online Dot de ¶ ¶
9 năm trước
$c = 57
$c = 58
$c = 59
500
501
$c = foo[]7
$c = foo[]8
504
505
$b = 50Oliver tại Hankeln-Online Dot de ¶ ¶
nháy mắt716 ¶
507
15 năm trước ¶
9 năm trước
508
509
510
$b = 50Oliver tại Hankeln-Online Dot de ¶ ¶
nháy mắt716 ¶
512
513
514
515
516
$b = 5015 năm trước ¶
21 năm trước
518
519
520
521
522
523
524
525
$b = 50Mattias tại mail dot ee ¶ ¶
20 năm trước
527
Chriswarbo tại Gmail Dot Com ¶ ¶
9 năm trước
528
529
$b = 50Oliver tại Hankeln-Online Dot de ¶ ¶
nháy mắt716 ¶
531
532
533
$b = 5015 năm trước ¶
nháy mắt716 ¶
535
536
537
538
539
540
$b = 5015 năm trước ¶
nháy mắt716 ¶
542
543
54415 năm trước ¶
9 năm trước
545
546
547
$b = 50Oliver tại Hankeln-Online Dot de ¶ ¶
9 năm trước
549
550
$b = 50Oliver tại Hankeln-Online Dot de ¶ ¶
nháy mắt716 ¶
552
553
554
555
556
557
$b = 5015 năm trước ¶
nháy mắt716 ¶
559
560
561
562
563
$b = 50