Q:

std::cin:: and why a newline remains

Reference Why is the Console Closing after I've included cin.get()?
I was utilizing std::cin.get()
#include<iostream>    

char decision = ' ';
bool wrong = true;

while (wrong) {
    std::cout << "\n(I)nteractive or (B)atch Session?: ";

    if(std::cin) {
        decision = std::cin.get();

        if(std::cin.eof())
            throw CustomException("Error occurred while reading input\n");
    } else {
        throw CustomException("Error occurred while reading input\n");
    }

   decision = std::tolower(decision);
   if (decision != 'i' && decision != 'b')
        std::cout << "\nPlease enter an 'I' or 'B'\n";
   else
        wrong = false;
}

I read basic_istream::sentry and std::cin::get.
I chose instead to use std::getline as the while loop is executing twice because the stream is not empty.
std::string line; std::getline(std::cin, line);

As the reference I posted above states within one of the answers, std::cin is utilized to read a character and std::cin::get is utilized to remove the newline \n.
char x; std::cin >> x; std::cin.get();

My question is why does std::cin leave a newline \n on the stream?

A:

Because that's its default behavior, but you can change it. Try this:
#include<iostream>
using namespace std;

int main(int argc, char * argv[]) {
  char y, z;
  cin >> y;
  cin >> noskipws >> z;

  cout << "y->" << y << "<-" << endl;
  cout << "z->" << z << "<-" << endl;
}

Feeding it a file consisting of a single character and a newline ("a\n"), the output is:
y->a<-
z->
<-

