Error in the Auto-Optimizer code

 
Hello everyone, I am having an error in writing the code attached below. Here is also a screenshot of the screen.

How could I correct the writing?

Thank you all.

Files:
 

You are defining a function. What does that return?

 ???   CAuto_optimizer::virtual_optimizer(void) {
 
William Roeder #:

You are defining a function. What does that return?


Basically the whole code is an automatic optimizer for working with logistic regression.


It is a ready-made code I am studying, so I don't know exactly what this line returns and why this error.


I welcome suggestions on how to solve this.


Thank you.

Reason: