PHP学习笔记运算符优先级

$t == 1 && $tt = 2

(($t == 1) && $tt) = 2

($t == 1) && ($tt = 2)

expr_without_variable: 
// 有隐规则存在, 相当于T_BOOLEAN_AND成为了"一元操作符". 
|   expr T_BOOLEAN_AND  { zend_do_boolean_and_begin(&$1, &$2 TSRMLS_CC); } exp

$result = mysql_query(*)  or die(mysql_error());

$person = $who or $person = "laruence";

$person = empty($who)? "laruence" : $who;

<?php

//随机生成一个4位数的数字验证码

$num=”";     for($i=0;$i<4;$i++){     $num .= rand(0,9);     }

//4位验证码也可以用rand(1000,9999)直接生成

//将生成的验证码写入session，备验证页面使用

Session_start();     $_SESSION["Checknum"] = $num;

//创建图片，定义颜色值     Header(“Content-type: image/PNG”);

srand((double)microtime()*1000000);

$im = imagecreate(60,20);

$black = ImageColorAllocate($im, 0,0,0);

$gray = ImageColorAllocate($im, 200,200,200);

imagefill($im,0,0,$gray);

//随机绘制两条虚线，起干扰作用

$style = array($black, $black, $black, $black, $black, $gray, $gray, $gray, $gray, $gray);

imagesetstyle($im, $style);

$y1=rand(0,20);     $y2=rand(0,20);     $y3=rand(0,20);     $y4=rand(0,20);

imageline($im, 0, $y1, 60, $y3, IMG_COLOR_STYLED);

imageline($im, 0, $y2, 60, $y4, IMG_COLOR_STYLED)

//在画布上随机生成大量黑点，起干扰作用;

for($i=0;$i<80;$i++)     {

imagesetpixel($im, rand(0,60), rand(0,20), $black);     }

//将四个数字随机显示在画布上,字符的水平间距和位置都按一定波动范围随机生成

$strx=rand(3,8);

for($i=0;$i<4;$i++){

$strpos=rand(1,6);     imagestring($im,5,$strx,$strpos, substr($num,$i,1), $black);     $strx+=rand(8,12);

}

ImagePNG($im);     ImageDestroy($im);

?>

<tr>

<td>验证码 :</td>

<td><input type=”text” name=”yzm”style=”width:60px;height:20px;” /><img src=”code.php” onclick=”javascript:this.src=’code.php?’+Math.random();”></img></td>

</tr>

<tr>    <td colspan=’2′><input type=”submit” value=”注册”/></td>

<td>验证码 :</td>

</tr>

Session_start();

//back_alert()验证码输入错误的时候，弹出错误信息

function back_alert($yzm){

echo “<script type=’text/javascript’>alert(‘$yzm’);history.back();</script>”;

}

//禁止恶意调用（禁止直接在浏览器打开post.php页面）

if($_POST["yzm"]==null){

back_alert(‘你都木有输入验证码，有木有？？？’);  }

// 禁止恶意注册

if(!($_POST["yzm"]==$_SESSION["Checknum"])){

back_alert(‘验证码不正确’);

} echo $_POST["yzm"];

<?php

$a=12;

function fn()
{
   global $a;//使用外层$a变量,不使用这个方法$a为局部变量
  $a+=12;
}

echo '$a='.$a//输出结果

?>

输出的结果:$a=24

 $glpbal $a;
 $a=123;

function f()
{
  echo $a;   //错误,
}

//再看看下面一例

 function f()
{
   global $a;
   $a=123;
}

f();
echo $a;  //正确,可以使用

//A.php 文件

<?php
function Test_Global()
{
    include 'B.php';
    Test();
}

$a = 0 ;
Test_Global();
echo $a;
?>

//B.php 文件

<?php
function Test()
{
   global $a;//申明函数体Sum内使用的$a变量为global全局变量
   $a =1;
}
?>

//A.php 文件

<?php
function Test_Global()
{
    Test();
}
include 'B.php'; //将include 从局部Test_Global函数中移出
$a = 0 ;
Test_Global();
echo $a;
?>

//B.php 文件

<?php
function Test()
{
    global $a;
    $a =1;
}
?>

for循环遍历方法
for($i=0;$i<count($arr);$i++){
echo '<br/>'.$arr[$i];
}

//while循环遍历方法
$i=0;//循环控制变量
while($i<count($colors)){
echo "<br/>".$colors[$i];
$i++;
}

//do..while
$i=0;//循环控制变量
do{
echo "<br/>".$colors[$i];
$i++;
}while($i<count($colors));

//foreach 遍历方法
这个foreach适用范围更广
foreach($arr as $key=>$val){
echo $key."=".$val."<br/>";
}

<?php
$arr_a = array(0 => "a", 1 => "b", 2 => "c");
$key = array_search("a", $arr_a);
if( $key !== FALSE ){
    echo "键名为：$key";
} else {
    echo '无匹配结果';
}
?>

$fruit["apple"] = "red";
$fruit["banana"] = "yellow";
$fruit["pear"] = "green";
if(array_key_exists("apple", $fruit)){
 printf("apple's color is %s",$fruit["apple"]);
}

<?php
$fruits = array("apple","banana","pear");
$numbered = array("1","2","3");
$cards = array_merge($fruits, $numbered);
print_r($cards);

// output
// Array ( [0] => apple [1] => banana [2] => pear [3] => 1 [4] => 2 [5] => 3 )
?>

<?php
$fruit1 = array("apple" => "red", "banana" => "yellow");
$fruit2 = array("pear" => "yellow", "apple" => "green");
$result = array_merge_recursive($fruit1, $fruit2);
print_r($result);

// output
// Array ( [apple] => Array ( [0] => red [1] => green ) [banana] => yellow [pear] => yellow )
?>   

<?php
$name = array("apple", "banana", "orange");
$color = array("red", "yellow", "orange");
$fruit = array_combine($name, $color);
print_r($fruit);

// output
// Array ( [apple] => red [banana] => yellow [orange] => orange )
?>

<?php

$fruits = array("Apple", "Banana", "Orange", "Pear", "Grape", "Lemon", "Watermelon");
$subset = array_slice($fruits, 3);
print_r($subset);

// output
// Array ( [0] => Pear [1] => Grape [2] => Lemon [3] => Watermelon )
?>

$arr = array(
‘d’ => array(‘id’ => 5, ‘name’ => 1, ‘age’ => 7),
‘b’ => array(‘id’ => 2,’name’ => 3,’age’ => 4),
‘a’ => array(‘id’ => 8,’name’ => 10,’age’ => 5),
‘c’ => array(‘id’ => 1,’name’ => 2,’age’ => 2)
);

function multi_array_sort($multi_array,$sort_key,$sort=SORT_ASC){
if(is_array($multi_array)){
foreach ($multi_array as $row_array){
if(is_array($row_array)){
$key_array[] = $row_array[$sort_key];
}else{
return false;
}
}
}else{
return false;
}
array_multisort($key_array,$sort,$multi_array);
return $multi_array;
}

//处理

echo “<pre/>”;
print_r(multi_array_sort($arr,’age’));exit;

//输出

Array
(
[c] => Array
(
[id] => 1
[name] => 2
[age] => 2
)

[b] => Array
(
[id] => 2
[name] => 3
[age] => 4
)

[a] => Array
(
[id] => 8
[name] => 10
[age] => 5
)

[d] => Array
(
[id] => 5
[name] => 1
[age] => 7
)

)

FOR ($i = 0; $i <= 2; $i++)
{
print "value is now " . $i . "<br>";
}

<html><body>
<?php $a=1;while($a<=5)  {  echo "The number is " . $a . "<br />";  $a++;  }?>
</body></html>

<html><body>
<?php $i=0;do  {  $i++;  echo "The number is " . $i . "<br />";  }while ($i<5);?>
</body></html>

goto a;

echo 'aa';

a:

echo 'bb';

<?php

       //第一种方法

       define("TAX_RATE",0.08);
       echo TAX_RATE;

       //第二种方法(php5.3)

       const TAX_RATE2=0.1;
       echo '-'.TAX_RATE2;

?>