Question

   #include <iostream>
    using namespace std;

    struct list
    {
        int data;
        list *next;
    };

    list *node, *tail = NULL, *head = NULL;
    void add2list();
    void extrem();

    int main()
    {
        add2list();
        extrem();

        return 0;
    }

    void add2list()
    {
        int input;
        cout << "Adding values to list :\n";
        cout << ">>";

        while(cin >> input)
        {
            node = new list;
            node->data = input;
            node->next = NULL;

            if (head == NULL)
            {
                head = node;
                tail = node;
            }
            else
             {
                tail->next = node;
                tail = node;
             }
        cout << ">>";
        }
    }

    void extrem()
    {
       int x, y;
       cin >> x >> y;
    }

when i run this program it’s only execute the add2list function ????

I’ve added cin.clear(), but the problem is not solved, why??

somecan give clear explaintion about how can I solve this

and When is the use of cin.clear() object useful؟؟

sorry 4 my bad english

Answer 1

There are two reasons why std::cin >> value can fail:

1. std::cin has reached its end (e.g. by using Ctrl-D or Ctrl-Z, depending on which system you are using)
2. The pending character cannot be parsed as a value, i.e., in your case as int. The offending character is, however, not extracted.

Obviously, there isn’t anything you can in the first situation: once you have reached the end of the standard input stream there is no way to extend it. So, let’s assume you entered an invalid character, e.g., a letter. Trying to read this letter as an int will fail and cause std::ios_base::failbit to be set. Before you can do anything to the stream you need to clear() it. Once you have cleared std::ios_base::failbit you can ignore() the next character and then try again. That is, if you add after your call do add2list() the following two calls things should be fine, assuming there is only one offending letter (otherwise you might need to ignore more characters):

std::cin.clear();
std::cin.ignore();