Generating ALL possible combinations

[proff.hacker]

Hi everybody,

I have an array of letter for example:

string strings[] = { "a", "b", "c", "d", "e"};

I want to generate all possible combinations of a specific length which is determined by the user, for example when he selects 3:

aaa
aab
aac
aad
aae
aba
abb
abc
abd
abe
abd
aca
acb
acc
acd
ace

etc...


I started by this code but it's limited to the length I assume before the runtime

foreach (string l1 in strings)
            {
                foreach (string l2 in strings)
                {
                    foreach (string l3 in strings)
                    {
                        myword = l1 + l2 + l3;
                    }
                }
            }

can you think of any solution that works with any length selected by the user at runtime?

Thanks