Opening files with variable name?

We're learning file I/O. The code below works, but the file name to open, testFile.txt, is hard coded into the program. How can the filename be input by the user? I'm not using argv stuff on the command line because the compiler we're using, MSVC 6.0 Intro edition, doesn't support release versions, only debug.
I've tried cin with strings and char * 's, but always get a compile error. Any ideas? Thanks.

Code:

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  fileIn1.open("testFile.txt");

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Inputting strings with cin is the way to go.

std::string blah;
cin >> blah;
std::ifstream fileIn1(blah.c_str());

Hadn't tried that, never used c_str(). I thought that was for converting C++ strings to C strings. I'll give it a try, thanks.