are there a similar functions to explode/implode in the .net-framework?
or do i have to code it by myself?
The current answers are not fully correct, and here is why:
all works fine if you have a variable of type string[], but in PHP, you can also have KeyValue arrays, let's assume this one:
$params = array(
    'merchantnumber' => "123456789", 
    'amount' => "10095", 
    'currency' => "DKK"
);
and now call the implode method as echo implode("", $params); your output is
12345678910095DKK
and, let's do the same in C#:
var kv = new Dictionary<string, string>() {
             { "merchantnumber", "123456789" },
             { "amount", "10095" },
             { "currency", "DKK" }
         };
and use String.Join("", kv) we will get
[merchantnumber, 123456789][amount, 10095][currency, DKK]
not exactly the same, right?
what you need to use, and keep in mind that's what PHP does, is to use only the values of the collection, like:
String.Join("", kv.Values);
and then, yes, it will be the same as the PHP implode method
12345678910095DKK
You can test PHP code online using http://WriteCodeOnline.com/php/
 
    
    There are two methods that correspond to PHP's explode and implode methods.
The PHP explode's equivalent is String.Split. The PHP implode's equivalent is String.Join.
 
    
    