Android programmers learn PHP development (3) - loop variables are true, false and not empty - PhpStorm

Because PHP was produced in 1994, its syntax is a mixture of C, Java, Perl and some of his own programming syntax.
So, students who have basic knowledge of Java before will not have too much trouble learning.

<?php
    /**
     * 变量名以$开始
     * 变量名区分大小写
     */
    $name = "iwanghang";

    for ($x=0; $x<=5; $x++) {
        echo $name .$x."<br>";
    }
    /** 上面的for循环的打印结果，如下：
        iwanghang0
        iwanghang1
        iwanghang2
        iwanghang3
        iwanghang4
        iwanghang5 */

    /**
     * var_dump 打印一个变量的类型和值
     * 看下面3个例子
     */
    var_dump($name); // 打印结果：string(9) "iwanghang"
    echo "<br>x = ".$x."<br>"; // 打印结果：x = 6
    var_dump($x); // 打印结果：int(6)
    echo "<br>";
    var_dump(666); // 打印结果：int(666)
    echo "<br>";

    /**
     * isset 判断真假
     */
    $nameInit = isset($name);
    var_dump($nameInit); // 打印结果：bool(true)
    echo "<br>";
    $nameInit1 = isset($name1);
    var_dump($nameInit1); // 打印结果：bool(false)
    echo "<br>";

    /**
     *  布尔值(真假)判断
     */
    if(isset($name)){
        echo "真<br>"; // 打印结果：真
    }else{
        echo "假<br>";
    }
    if(isset($name1)){
        echo "真<br>";
    }else{
        echo "假<br>"; // 打印结果：假
    }

    /**
     * 为空判断
     */
    if(empty($name)){
        echo "空<br>";
    }else{
        echo "非空<br>"; // 打印结果：非空
    }
    if(empty($name1)){
        echo "空<br>"; // 打印结果：空
    }else{
        echo "非空<br>";
    }

    /**
     * x等于6
     * empty($x)为非空
     * var_dump(empty($x))返回布尔值为假
     *
     * x1不存在
     * empty($x1)为空
     * var_dump(empty($x1))返回布尔值为真
     */
    echo $x."<br>"; // 打印结果：6
    echo "".empty($x)."<br>"; // 打印结果：
    var_dump(empty($x)); // 打印结果：bool(false)
    echo "<br>------<br>";

    echo "".empty($x1)."<br>"; // 打印结果：1
    var_dump(empty($x1)); // 打印结果：bool(true)

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