inFile.open Help

I am trying to read a file but I would like the user to enter the name of the file. This is the code that works when you add a static file into the code.

Code:

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    inFile.open (xyz.txt);
    inFile >> length;
    inFile.close ();

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This is what I would like for the user to enter in the file name, but it does not work.

Code:

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    cout << "Enter The Name Of the File"<< endl;
    cin >> input;
    inFile.open (input);
    inFile >> length;
    inFile.close ();

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Thanks for your time and help.