Read One Integer from a File

A text file starts with a whole number, for example:

42

Write a function int readNumber(const string& filename) that returns the first integer stored in the file. The starter already opens the file as ifstream in and declares int n = 0; add the one line that reads an integer from in into n with >>. Only the first number matters even if the file contains more, and it may be negative.

The test prints the returned value on its own line, for example (see Expected Output).

Do NOT write a main function.