Ensure queue is in ascending order

Question

The program reads in a queue of integers and returns determines whether or not it is valid (ascending). How can this code be improved? I assume iterator include statement is unnecessary?

#include <iostream>
#include <queue>
#include <deque>
#include <iterator>

template<typename T, typename Container=std::deque<T> >
class iterable_queue : public std::queue<T,Container>
{
public:
    typedef typename Container::iterator iterator;
    typedef typename Container::const_iterator const_iterator;

    iterator begin() { return this->c.begin(); }
    iterator end() { return this->c.end(); }
    const_iterator begin() const { return this->c.begin(); }
    const_iterator end() const { return this->c.end(); }
};

bool checkValidity(iterable_queue<int>& q) {
    if (q.empty() || q.size() <= 1){
        std::cout << "invalid entry, insufficient elements" << '\n';
        return false;
    }
    while(q.size()){
        auto i = q.begin();
        auto j = ++q.begin();
        for(; i < q.end() && j < ++q.end();){
            std::cout << *i << " " << *j << '\n';
            if (*(i) > *(j)) {
                std::cout << "invalid entry, not properly sorted" << '\n';
                return false;
            }
            i++, j++;
        }   
        std::cout << "valid entry, properly sorted" << '\n';
        return true;
    }
    std::cout << "invalid entry, insufficient elements" << '\n';
    return false;
}

const char* bool_cast(const bool b) {
    return b ? "true" : "false";
}        

int main () {
    iterable_queue<int> numbers;
    int temp;

    std::cout << "Pushing..." << '\n';
    while(temp >= 0){
        std::cout << "Enter numbers: ";
        std::cin >> temp;
        if(temp >= 0){
            numbers.push(temp);
        }
    }

    bool ck = checkValidity(numbers);
    std::cout << bool_cast(ck) << '\n';

    std::cout << "{ ";
    while(numbers.size() > 0){
        std::cout << numbers.front();
        numbers.pop();
        std::cout << " ";
    }
    std::cout << "}" << '\n';

    return 0;
}

Answer 1

Queues are not designed to be used like this. Your iterable_queue clearly shows that you are not using queues the way they are supposed to be used. And the checkValidity function should be simplified with std::is_sorted from the standard library. In q.empty() || q.size() <= 1, the first condition is subsumed by the second. The while(q.size()){ loop also seems to have no significance. ++q.end() is also undefined behavior. The bool_cast functionality is already provided by std::boolalpha.

Overall, I think you are seriously over-complicating everything:

#include <algorithm>
#include <iostream>
#include <iterator>
#include <vector>

int main()
{
    std::vector<int> numbers;
    for (int num; std::cin >> num && num >= 0;) {
        numbers.push_back(num);
    }

    bool valid = numbers.size() > 1 && std::is_sorted(numbers.begin(), numbers.end());
    std::cout << "Valid? " << std::boolalpha << valid << '\n';

    std::cout << "{ ";
    for (int num : numbers) {
        std::cout << num << ' ';
    }
    std::cout << "}\n";
}

(live demo)