簡化if語句中的PHP

Question

是否可以簡化一系列用於構建URL參數的if語句？我怎麼會在第一個參數前添加一個?，其餘的&，$var1也可能是0？

這裏是我想要做的一個例子：

<?php 
$var1 = 1; 
$var2 = 1; 
$var3 = 0; 
$var4 = 1; 

$urlparam = ""; 
if ($var1 == 1) $urlparam = $urlparam . "?var1=".$var1; 
if ($var2 == 1) $urlparam = $urlparam . "&var2=".$var2; 
if ($var3 == 1) $urlparam = $urlparam . "&var3=".$var3; 
if ($var4 == 1) $urlparam = $urlparam . "&var4=".$var4; 

echo "http://example.com/index.php" . $urlparam; 
// http://example.com/index.php?var1=1&var2=1&var4=1 
?> 

Answer 1

$vars = array(
    'var1' => 1, 
    'var2' => 1, 
    'var3' => 0, 
    'var4' => 1 
); 
$vars = array_filter($vars); 
$urlparam = '?' . http_build_query($vars); 

1. $vars持有的值的數組，我們可以把它放到我們的查詢字符串
2. array_filter()刪除任何與零（假）值
3. 使用http_build_query()爲我們建立查詢字符串使用餘下的值