I can tell to terminate the std::cin an invalid character like feeding string when int expected or ctrl d or crtl z depending on the platform but why not just a simple enter won't do the job? Is asking user to enter an invalid or a special character to end the input plausible in real world applications? How is this situation handled in professional applications? An example from c primer below:

#include <iostream>

int main()
{
    int currVal = 0;
    int val = 0;

    if (std::cin >> currVal)
    {
        int cnt = 1;
        while (std::cin >> val)
        {

            if (currVal == val)
            {
                  cnt;
            }
            else
            {
                std::cout << "the number " << currVal << " occurs " << cnt << " times " << std::endl;
                currVal = val;
                cnt = 1;
            }
        }
        std::cout << "the number " << currVal << " occurs " << cnt << " times " << std::endl;
    }
    return 0;
}

I have to do ctrl d twice to program to finish for the input of 11 11 22 22 if I don't press enter first. Any suggestion is welcome, thank you for your time.