3digitNumberEnter

#include <iostream>

int main()
{
    int num{ 0 };
    bool incorrectNumber{ false };

    do
    {
        std::cout << "Enter some numer 0-999\n";
        std::cin >> num;

        //flag = !(num >= 0 and num <= 999);
        incorrectNumber = num < 0 or num > 999;

        if (incorrectNumber)
        {
            std::cout << "Incorrect number!\Try again!\n";
        }

    } while (incorrectNumber);

    std::cout << "Good number is: " << num << '\n';
}