如何通过URL设置PHP变量？

I'm trying to cause a variable $btn1Pressed to be set via a URL load. For example, loading http://mywebsite.com/myphp.php?btn1Pressed=1 would set the variable to 1. The below test code doesn't seem to be doing anything:

<?php
    if ($btn1Pressed == 1) {
        echo 'Button One Pressed'; 
    }

    else{
        echo 'Button Two Pressed'; 
    }
?>

Before the vampires arrive...

<?php
    if (isset($_GET['btn1Pressed']) && $_GET['btn1Pressed'] == 1) {
        echo 'Button One Pressed'; 
    }

    else{
        echo 'Button Two Pressed'; 
    }
?>

Anything in the query string will be in PHP's $_GET array. To see the entire array you can print_r($_GET); in your PHP code. In the example I am also testing to make sure the variable has been set, for safeties sake. You should never accept user input without sanitizing, which I have not done here.

You can also set a variable with the array item:

$btn1Pressed = $_GET['btn1Pressed'];

You can try use GET method:

if ($_GET['btn1Pressed'] == 1) {
    echo 'Button One Pressed';
}
else{
    echo 'Button Two Pressed'; 
}

<?php

$btn_pressed = filter_input(INPUT_GET, 'btn1Pressed',  FILTER_SANITIZE_NUMBER_INT);

if ($btn_pressed == 1) {
    echo 'Button One Pressed';
} else {
echo 'anything';
}
?>