php运算符

php 
/*    算数运算符
    $x=10; 
    $y=6;
    echo ($x + $y); // 输出16
    echo ‘
‘;  // 换行
     
    echo ($x - $y); // 输出4
    echo ‘
‘;  // 换行
     
    echo ($x * $y); // 输出60
    echo ‘
‘;  // 换行
     
    echo ($x / $y); // 输出1.6666666666667
    echo ‘
‘;  // 换行
     
    echo ($x % $y); // 输出4
    echo ‘
‘;  // 换行
     
    echo -$x;

php赋值运算符
    $x=10;

    $k=15;
    $k %=4;//$k=$k%4
    echo $k;

    $a = "Hello";
    $b = $a."world!";
    echo $b;//输出Hello world!

    $x="Hello";
    $x.="world!";//$x =$x."world!";
    echo $x;//输出Hello world!

    $x=10; 
    echo ++$x; // 输出11
     
    $y=10; 
    echo $y++; // 输出10
     
    $z=5;
    echo --$z; // 输出4
     
    $i=5;
    echo $i--; // 输出5
*/
//三元运算符
    $test = ‘菜鸟教程‘;
    $test = null;//$test赋值为空 取消设置
    //isset检测变量是否设置 返回布尔类型
    var_dump(isset($test));
    if(isset($test)){
        echo "yyyyyyyy";
    }
    else{
        echo "nnnnnnn";
    }


    //$test = "菜鸟教程";
    //$test = null;
    //$username = isset($test) ? $test:"abc";
    //echo $username;
    $test = "123";
    $username;
    if(isset($test)){
        $username = $test;
    }
    else{
        $username = "abc";
    }
    echo $username;
?>