Is this a good practice to check user input?

Question

do {
    std::cout << "Enter a valid name" << std::endl;
    std::cin >> name;

} while (!validName(name) && std::cout << "It is not a valid name" << std::endl);

Is this a good practice tha if the name is not valid, then I respond with a line this way?

Answer 1

It's probably clearer to do the checking and output within the loop itself. You can do this by breaking an infinite loop or continuing a one-time loop. For example:

do {
    std::cout << "Enter a valid name" << std::endl;
    std::cin >> name;
    if (!validName(name)) {
        std::cout << "It is not a valid name" << std::endl;
        continue;
    }
} while (false);

Or the reverse:

for ( ;; ) {
    std::cout << "Enter a valid name" << std::endl;
    std::cin >> name;
    if (validName(name))
        break;

    std::cout << "It is not a valid name" << std::endl;
}

I generally prefer the second, since it makes it easy to inject a counter, so you can do some other type of error handling if the loop body fails more than a certain number of times.

for (int attempt = 0; attempt < 3; ++attempt) {
    std::cout << "Enter a valid name" << std::endl;
    std::cin >> name;
    if (validName(name))
        break;

    std::cout << "It is not a valid name" << std::endl;
}

if (!validName(name)) {
    std::cout << "Failed to get a valid name after 3 tries" << std::endl;
    std::abort();
}