hmm... it looks like you are trying to use classes by treating the class name as the name of a function (the constructor), and then attempting to do procedural programming.
What you should do is to determine what you want to model. What is a GameManager? What is it for, and what does it do? Answering this would allow you to design its member functions, especially its public interface. From there you can determine what it must keep track of, and thus decide on what its member variables should be.
Instead of invoking the constructor by treating it as no more than a function call, you would create an object, and use that object. The constructor is just to initialise the state of that object.