PHP入门：从基础语法开始学习

<?php    echo "Hello World!";    print "Hello World!";?>

<?php     # This is a comment    // This is another comment?>

<?php    $name = "Tom";    $age = 25;    $height = 170.5;?>

<?php    $num1 = 10; // 整型    $num2 = 3.14; // 浮点型    $truth = true; // 布尔型    $name = "John"; // 字符串    $arr = array("苹果", "香蕉", "橙子"); // 数组    $obj = new stdClass(); // 对象    $nothing = null; // NULL?>

<?php    $num1 = 10;    $num2 = 3;    $sum = $num1 + $num2; // 加法运算符，值为13    $diff = $num1 - $num2; // 减法运算符，值为7    $prod = $num1 * $num2; // 乘法运算符，值为30    $quo = $num1 / $num2; // 除法运算符，值为3.33...    $mod = $num1 % $num2; // 取模运算符，值为1    $cond = ($num1 > $num2); // 比较运算符，值为true    $logic = ($num1 > 0) && ($num2 < 5); // 逻辑运算符，值为false?>

<?php    $greeting = "Hello";    $name = "Tom";    $message = $greeting . $name; // $message的值是"HelloTom"?>

<?php    $num = 10;    if ($num > 0){        echo "这个数是正数";    }    elseif ($num == 0){        echo "这个数是零";    }    else{        echo "这个数是负数";    }?>

<?php    for ($i = 1; $i <= 10; $i++){        echo $i." ";    }    echo "<br>";    $j = 1;    while ($j <= 10){        echo $j." ";        $j++;    }?>

<?php    function square($num){        return $num * $num;    }    $result = square(5);    echo $result; // 输出25?>