Persistent Counter

Write a function int incrementCounter(const string& filename) that:
1. tries to open filename for reading (ios::in) and read one integer from it;
2. if the file could be opened and an integer was read, the new value is that integer plus 1; otherwise (the file does not exist or is empty) the new value is 1;
3. opens the file in ios::out | ios::trunc mode, writes the new value to it, and returns the new value.

The test prints each returned value on its own line. If the file contains 5, one call prints the output shown in Expected Output.

If the file does not exist, the first call prints 1 and a second call then prints 2:
1
2

Do NOT write a main function.