I'm a member of codeforces for a while now, and I'm familiar with format of contests, website interface etc. I have seen this post about tomorrow's SRM on topcoder and I've decided to participate in. Do I need to register for the contest as in codeforces' rounds? And it also seemed like I can't use my own editor on arena. Do I have to use the coding area to code the solution? Is there an option or workaround not to use its built-in editor? I'm also curios which one's (topcoder or codeforces) type of problems more similar to IOI?
Yes, you need to register.
Yes can use your own editor, but you need to install special plugin.
What's name of the plugin?
Plugin
But there are a lot of plugins and you can choose any plugin you want
Another option (if you're too lazy to install plugins) is to simply use your favorite editor and then copy-paste to built-in editor.
I think that CF problems are more similar to IOI than TC ones.