while(std :: cin>>值)如何工作?

在C ++ Primer中给出的示例中，

In an example given in C++ Primer,

#include <iostream>
using namespace std;

int main() {
    int sum = 0, value = 0;  
    while (std::cin >> value) {       
        sum += value; // equivalent to sum = sum + value
    }    
    std::cout << "Sum is: " << sum << std::endl;    
    return 0; 

}

(std :: cin >>值)如何返回true?什么是文件结尾"?看来我必须理解该术语才能理解我的主要问题.

How does (std::cin >> value) return true? And what is an "End Of File"? It seems that I must understand that term in order to understand my primary question.

谢谢！