How to check if the input is a valid integer without any other chars?

Question

#include 
#include 

using namespace std;

int main()
{
    int x;
    cout << \"5 + 4 = \";
    while(!(cin >> x)){
               


        

Answer 1

If you can use C++11 (and your compiler has full regex support), you can also use the library:

#include 
#include 
#include 
#include 
#include 

int main()
{
    std::string line;
    std::pair value = std::make_pair(0, false);
    std::cout << "5 + 4 = ";
    while (!value.second)
    {
        while (!std::getline(std::cin, line))
        {
            std::cout << "Error, please try again." << std::endl;
            std::cin.clear();
            std::cin.ignore(std::numeric_limits::max(), '\n');
        }

        if (!std::regex_match(line, std::regex("(\\+|-)?[[:digit:]]+")))
        {
            std::cout << "Error, please try again." << std::endl;
        }
        else
        {
            value = std::make_pair(std::stol(line), true);
        }
    }

    if (value.first == (5 + 4))
    {
        std::cout << "Correct!" << std::endl;
    }
    else
    {
        std::cout << "Incorrect!" << std::endl;
    }

    return 0;
}