How does while (std::cin >> value) work?

Question

In an example given in C++ Primer,

#include 
using namespace std;

int main() {
    int sum = 0, value = 0;  
    while (std::cin >> va         


        

Answer 1

The overloaded operator>> function returns a reference to the stream itself, and the stream have an overloaded operator that allows it to be used in a boolean condition to see if the last operation went okay or not. Part of the "okay or not" includes end of file reached, or other errors.

Answer 2

C++ translates this line

while (std::cin >> value)

to something like

inline bool f(int v) {
  auto& i = std::cin >> v;
  return i.operator bool();
}

while( f(v) ) {

Why it translates to bool? Because while expects a boolean expression, so compiler search for the boolean conversion operator of the return of std::cin >> v.

What is a bool conversion operator? Boolean conversion operator translates the object to bool. If some part of the code expect to some type to work a as boolean (like casting) then this operator is used.

What is an operator? Is a function or method that override the behavior of some operationg expressions (+, -, casting, ->, etc)

Answer 3

If you are a beginner you don't need to write

std::

---

everytime. If you have written:

using namespace std;

---

it would do the trick. I hope you got the point. :)