fstream file variable?

Is there a way to have the user specify what he wants the file to be called that he is creating and appending to? For example...

string filename;
ofstream blah;

cout << "file name?\n";
cin >> filename;

blah.open("filename.txt",ios::app);

but instead of "filename.txt" it has whatever the user typed in and then ".txt" Thanks.

-andy

Have you tried this:
blah.open(filename.c_str(),ios::app);

Well I'll be.. Thanks man..but how do I get a .txt at the end of that baby on the same line?

EDIT: I concactinated (however you spell that word) it with another string with a value of ".txt" It worked but im hoping i can add it on the same line as the variable.

Either:
filename += ".txt";
blah.open(filename.c_str(),ios::app);

or:
blah.open(string(filename + ".txt").c_str(), ios::app);

or even:
blah.open((filename + ".txt").c_str(), ios::app);

Take your pick!

scorp..have I ever told you i loved you? (in a non-gay way)

THANKS MAN!
-andy