php - PHP：如何初始化变量？

Question

我有一个问题要问你，希望你能帮助我。我想写计算器但我没有机会改变操作，我只能使用加法操作。我不知道发生了什么。谁能帮我？

看看它，发生了什么？

<?php
$x = isset($_POST['field']);
if($x == 1){ 
    echo $x + 5;
}
elseif($x == 2){
    echo $x - 5;
}
?>

Answer 1

You code is wrong as this line will evaluate only as 0 (false) or 1 (true) if condition is met:

$x = isset($_POST['field']);  

You need to do it that way:

$x = isset($_POST['field']) ? $_POST['field'] : 0;

(where 0 is default value, $x is assigned to in case there's no $_POST['field]` set.

Answer 2

$x = isset($_POST['field']) ? (int)$_POST['field'] : 0;

You want the value, not the boolean if it's set or not.