Why does program crash when I give input to a dynamically allocated array in C++

<pre lang="C++">
#include <iostream>
#include <vector>
#include <initializer_list>
using namespace std;

template <typename T>
class greater_than{
private:
    const T& value;
public:
    greater_than(T& val) : value(val) {}
    bool operator() (const T& val) {return val > value;}
};

template <typename T>
class scores {
private:
    T* myscores;
    int size;
public:
    T& operator[](int& i) {
        return myscores[i];
    }
    ~scores() {delete[] myscores;}
    scores() : myscores{new T[1]}, size{0} {}
    scores(initializer_list<t> vals) : myscores{new int[vals.size()]}, size{int(vals.size())} {
        copy(vals.begin(), vals.end(), myscores);
    }
    scores(scores& val) : myscores{new T[val.size]}, size{val.size} {
        for (int i = 0; i < val.size; ++i) {
            myscores[i] = val[i];
        }
    }
    
    void push_back(istream& is) {
        int values;
        while (is >> values) {
            myscores[size] = values;
            ++size;
        }
    }
    int getsize() {
        return size;
    }
    
    T* begin() const{
        return size ? &myscores[0] : nullptr;
    }
    
    T* end()  const {
        return size ? &myscores[size] : nullptr;
    }
    friend ostream& operator<<(ostream& os, scores& mys);
    
};
ostream& operator<<(ostream& os, scores<int>& mys) {
    for (int i = 0; i < mys.size; ++i) {
        os << mys.myscores[i] << " ";
    }
    return os;
}

template<typename T>
T* begin(scores<t>& x) {
    return x.size ? &x[0] : nullptr;
}

template<typename T>
    T* end(scores<t>& x) {
        return x.size ? &x[0]+x.size() : nullptr;
    }

template <typename container, typename holdresult>
holdresult sum(const container& mycon, holdresult value = 0) {
    for (auto& x : mycon)
        value += x;
    return value;
}

template <typename con, typename pred>
int countp(const con& vec, pred predicate) {
    int cnt = 0;
    for (auto x : vec)
        if (predicate(x))
            ++cnt;
    return cnt;
}
int main()
{
    scores<int> myval {0};
    while (cin) {
        myval.push_back(cin);
    }
    for (auto x : myval)
        cout << x << " ";
}