php array traversal skills

* Array traversal

* 1. foreach($arr as $key => $value) {}

* 2. Principle: Array $arr according to key value pair in sequence Take it out into $key=>$value and process it one by one, similar to callback

* 3. If you only process the value, you can omit $key: foreach($arr as $value) {}

* 4. Especially suitable for associative arrays, of course also suitable for index arrays

$teacher = ['id'=>1001, 'name'=>'peter zhu', 'salary'=> 3000, 'course'=>'php'];

//Use for loop to implement traversal of associative array

for ($i=0; $i<count($teacher); $i++) {
echo key($teacher),&#39;=>&#39;,current($teacher),&#39;<br>&#39;;
next($teacher);
}
echo &#39;<hr color="red">&#39;;

//Use while loop to implement

reset($teacher);
$i = 0;
while ($i<count($teacher)) {
echo key($teacher),&#39;=>&#39;,current($teacher),&#39;<br>&#39;;
next($teacher);
$i++;
}
echo &#39;<hr color="red">&#39;;
//foreach($arr as $key=>$value):数组专用的遍历语法结构
echo &#39;<h4 id="讲师信息">讲师信息</h4>&#39;;
echo &#39;<ul>&#39;;
foreach ($teacher as $key => $value) {
    echo &#39;<li>&#39;.$key.&#39;:&#39;.$value.&#39;</li>&#39;;
}
echo &#39;</ul>&#39;;
echo &#39;<hr color="red">&#39;;
//如果只对值感兴趣
echo &#39;<table border="1" cellpadding="3" cellspacing="0" width="300">&#39;;
echo &#39;<caption>讲师信息表</caption>&#39;;
echo &#39;<tr bgcolor="lightskyblue"><th>ID</th><th>姓名</th><th>工资</th><th>课程</th></tr>&#39;;
echo &#39;<tr>&#39;;
foreach ($teacher as $value) {
    echo &#39;<td align="center">&#39;.$value.&#39;</td>&#39;;
}
echo &#39;</tr>&#39;;
echo &#39;</table>&#39;;
echo &#39;<hr color="red">&#39;;

//Create a date picker

echo '

Select your birthday:

';

//Generate year

$years = range(1980, 2000);
echo &#39;<select name="year">&#39;;
foreach ($years as $value) {
    echo &#39;<option>&#39;.$value.&#39;年</option>&#39;;
}
echo &#39;</select>&#39;;
echo &#39;  &#39;;

//Generation month

$months = range(1, 12);
echo &#39;<select name="months">&#39;;
foreach ($months as $value) {
    echo &#39;<option value=&#39;.$value.&#39;>&#39;.sprintf("%02d",$value) .&#39;月</option>&#39;;
}
echo &#39;</select>&#39;;
echo &#39;  &#39;;

//Generation day

$days = range(1, 31);
echo &#39;<select name="days">&#39;;
foreach ($days as $value) {
    echo &#39;<option value=&#39;.$value.&#39;>&#39;.sprintf("%02d",$value) .&#39;日</option>&#39;;
}
echo &#39;</select>&#39;;
echo &#39;  &#39;;
echo &#39;<button>提交</button>&#39;;