php语法

类型：

　　四种标量类型：boolean, integer, float, sring

　　两种符合类型：array, object

　　如过要将一个变量轻质转换成某类型，可以使用settype() 函数

<?php
$bool = TRUE; // a boolean
$str = "foo"; // a string
$int = 12; // an integer

echo gettype($bool); // prints out "boolean"
echo gettype($str); // prints out "string"

// If this is an integer, increment it by four
if (is_int($int)) {
 $int += 4;
}

// If $bool is a string, print it out
// (does not print out anything)
if (is_string($bool)) {
 echo "String: $bool";
}
?>

变量：

　　一个美元符号后面跟上一个变量名，大小写敏感，一个有效的变量名由字母或者下划线开头，后面跟上任意数量的字母、数字或者下划线

　　传值方式有：传值赋值、传地址赋值

<?php
$foo = 'Bob'; // Assign the value 'Bob' to $foo
$bar = &$foo; // Reference $foo via $bar.
$bar = "My name is $bar"; // Alter $bar...
echo $bar;
echo $foo; // $foo is altered too.
?>

常量：

　　常量用define()函数来定义，一个常量一旦被定义就不能再改变或者取消定义

　　常量只能包含标量数据：boolean, integer, float, string

　　常量和变量不同：

- 　　常量前面没有美元符号（$）；
- 　　常量只能用 define() 函数定义，而不能通过赋值语句；
- 　　常量可以不用理会变量范围的规则而在任何地方定义和访问；
- 　　常量一旦定义就不能被重新定义或者取消定义；
- 　　常量的值只能是标量。
- <?php
 define("CONSTANT", "Hello world.");
 echo CONSTANT; // outputs "Hello world."
 echo Constant; // outputs "Constant" and issues a notice.
 ?>

表达式：

　　表达式是php最重要的基石

<?php
function double($i)
{
 return $i*2;
}
$b = $a = 5; /* assign the value five into the variable $a and $b */
$c = $a++; /* post-increment, assign original value of $a
 (5) to $c */
$e = $d = ++$b; /* pre-increment, assign the incremented value of
 $b (6) to $d and $e */

/* at this point, both $d and $e are equal to 6 */

$f = double($d++); /* assign twice the value of $d before
 the increment, 2*6 = 12 to $f */
$g = double(++$e); /* assign twice the value of $e after
 the increment, 2*7 = 14 to $g */
$h = $g += 10; /* first, $g is incremented by 10 and ends with the
 value of 24. the value of the assignment (24) is
 then assigned into $h, and $h ends with the value
 of 24 as well. */
?>

运算符：

流程控制：
　　任何php脚本都是由一系列语句构成的，一条语句可以是一个赋值语句、一个函数调用、一个循环甚至一个什么也不做的条件语句。语句通常以分号结束。

<?php
if ($a > $b) {
 print "a is bigger than b";
} elseif ($a == $b) {
 print "a is equal to b";
} else {
 print "a is smaller than b";
}
?>

　　流程控制的代替语法，包括 if，while，for，foreach 和 switch。替代语法的基本形式是把左花括号（{）换成冒号（:），把右花括号（}）分别换成endif;，endwhile;，endfor;，endforeach; 以及 endswitch;

<?php
if ($a == 5):
 print "a equals 5";
 print "...";
elseif ($a == 6):
 print "a equals 6";
 print "!!!";
else:
 print "a is neither 5 nor 6";
endif;
?>
<?php
do {
 if ($i < 5) {
 print "i is not big enough";
 break;
 }
 $i *= $factor;
 if ($i < $minimum_limit) {
 break;
 }
 print "i is ok";

 /* process i */

} while(0);
?>
foreach (array_expression as $value) statement
```
foreach (array_expression as $key => $value) statement
```
<?php
/* foreach example 1: value only */

$a = array (1, 2, 3, 17);

foreach ($a as $v) {
 print "Current value of $a: $v. ";
}

/* foreach example 2: value (with key printed for illustration) */

$a = array (1, 2, 3, 17);

$i = 0; /* for illustrative purposes only */

foreach ($a as $v) {
 print "$a[$i] => $v. ";
 $i++;
}

/* foreach example 3: key and value */

$a = array (
 "one" => 1,
 "two" => 2,
 "three" => 3,
 "seventeen" => 17
);

foreach ($a as $k => $v) {
 print "$a[$k] => $v. ";
}

/* foreach example 4: multi-dimensional arrays */

$a[0][0] = "a";
$a[0][1] = "b";
$a[1][0] = "y";
$a[1][1] = "z";

foreach ($a as $v1) {
 foreach ($v1 as $v2) {
 print "$v2 ";
 }
}

/* foreach example 5: dynamic arrays */

foreach (array(1, 2, 3, 4, 5) as $v) {
 print "$v ";
}
?>
continue 接受一个可选的数字参数来决定跳过几重循环到循环结尾。continue 语句作用到 switch 上的作用类似于 break。如果你在循环中有一个 switch 并希望 continue 到外层循环中的下一个轮回，用 continue 2
<?php while (list ($key, $value) = each ($arr)) {
 if (!($key % 2)) { // skip odd members
 continue;
 }
 do_something_odd ($value);
}

$i = 0;
while ($i++ < 5) {
 echo "Outer ";
 while (1) {
 echo "  Middle ";
 while (1) {
 echo "  Inner ";
 continue 3;
 }
 echo "This never gets output. ";
 }
 echo "Neither does this. ";
}
?>

declare

require()

include()

require once()

include once()