Reuse One fstream Object

The program below opens data.txt for writing with an fstream, writes the number 42, and later reads a number back from the same stream object. Complete it so that, between the write and the read, it:
1. closes the stream with f.close(),
2. reopens the same file on the same object with f.open("data.txt", ios::in).

The read and the final print are already written. The program must print exactly the output shown in Expected Output.