How do I check a valid user input?

Question

I was doing a project for an online course and the final project was to make a Build Your Adventure program where the user has choices and they lead to endings. I deleted the huge intro and just now copied the part where I have the first choice. So basically, it all works when I don't write valid numbers, but when I write in a letter... the whole program begins an infinite loop. Please help: Here is the code:

#include <iostream>

int main() {

    int c1;

    std::cout << "After what felt like thirty minutes of "
                 "walking you reached a wall. Yes, a wall.\n"
                 "A wall so tall and wide you couldn't imagine "
                 "climbing over it or walking around it.\n";
    std::cout << "Luckly, you see two animals willing to help you.\n"
                 "1) A mole that can build a tunnel under the wall\n"
                 "2) An eagle that can carry you over the wall\n";
    std::cout << "Enter 1 or 2 to make a choice: ";
    std::cin >> c1;

    while (!(std::cin >> c1) || c) {
        std::cout << "Error! Please enter a valid input!\n";
        std::cout << "Enter 1 or 2 to make a choice: ";
        std::cin >> c1;
        std::cout << "\n"
    }

Answer 1

When you input invalid inputs for int , the stream goes into failed state and can't read further inputs. So you have to clear the error state of the stream and ignore anything left in the input stream.

#include <iostream>
#include <limits>

int main() {

    int c1;

    while (true)
    {
        std::cout << "Enter 1 or 2 to make a choice: ";

        if ((std::cin >> c1) && (c1 == 1 || c1 == 2)) break;
        std::cin.clear();
        std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
        std::cout << "Error! Please enter a valid input!\n";
    }

    // Now c1 is either 1 or 2 
}