// return size of an array as a compile-time constant. (The
// array parameter has no name, because we care only about
// the number of elements it contains.)
template<typename T, std::size_t N>                 // see info
constexpr std::size_t arraySize(T (&)[N]) noexcept  // below on
{                                                   // constexpr
  return N;                                         // and
}                                                   // noexcept

int keyVals[] = { 1, 3, 7, 9, 11, 22, 35 };      // keyVals has
                                                 // 7 elements

int mappedVals[arraySize(keyVals)];

A study of webrtc security
http://webrtc-security.github.io

Salting
https://auth0.com/blog/adding-salt-to-hashing-a-better-way-to-store-passwords/

https://excitel.net/en/page/about

Application states could be briefly described as below:

iOS Application Life Cycle Example

https://sourcemaking.com/design_patterns/

Necessary tools:
https://github.com/noodlewerk/NWPusher

https://sourcemaking.com/design_patterns/to_kill_a_singleton

In this post, it is explained how to properly use of singleton in view controllers. It basically uses dependency injection on singleton instances.
https://www.jessesquires.com/blog/refactoring-singletons-in-swift/