Given a number n, print n-th Fibonacci Number
What is the difference between mutex and critical section? Please explain from  Linux, Windows perspectives? 
I am programming in C#, would these two terms make a difference. Please post as much as  you can, with examples and such....
Thanks,
Robert
In the context of concurrent programming, both mutexes and critical sections are synchronization primitives used to ensure that multiple threads access shared resources in a controlled and safe manner. However, there are some subtle differences between the two.

A critical section is a region of code where access to a shared resource is mutually exclusive. It is a programming construct used to indicate to the compiler or runtime system that a certain block of code must be executed atomically, without interference from other threads. When entering a critical section, the thread acquires exclusive ownership of the critical section and prevents other threads from
I saw this video where someone says that electromagnetic wave is a chain reaction of electric and magnetic fields creating each other so the chain of wave moves forward.
I wonder where the photon is in this explanation. What is the relation between electromagnetic wave and photon?
I know that photon is a particle and of electromagnetic wave but can not understand the of wave and particle together. Like, Wave travels as wave but it behaves like a particle in certain conditions. Am I thinking too abstract? Can anyone explain with examples? Thanks for help