example_dynamic_container

#include <iostream>
using namespace std;

class Tst {
    int i;
    double d;
    static int n;
public :
    Tst() {
        i = ++n;
        d = 10*rand()/RAND_MAX;
    }
    Tst( int i, double d ):i(i),d(d){}
    bool operator<(const Tst& b)const {
        return d < b.d;
    }
    bool operator==(const Tst& b)const {
        return d == b.d;
    }
    ostream& ins(ostream& os) {
        os<< i << " " << d << endl;
        return os;
    }
};
int Tst::n = 0;
ostream& operator<<(ostream& os, Tst& x) {
    return x.ins( os );
}

template <class T> class DArray {
    unsigned sz, cap;
    T *r;
public:
    class IndexError {
        int r, i;
    public:
        IndexError(int r, int i):r(r), i(i) {}
        ostream& rep(ostream& os) {
            os<<"Index= "<< i <<"should be >=0 and <"<< r << endl;
            return os;
        }
    };

    class iterator;
    friend class iterator;
    class iterator {
        unsigned index;
        DArray &p;
    public:
        iterator(DArray& p, unsigned index =0):p(p),index(index) {}
        T& operator*(){ return p.r[index]; }
        iterator& operator++() {
            if(index<p.sz) index++;
            return *this;
        }
        iterator& operator++(int) {
            iterator x(p, index);
            if(index<p.sz) index++;
            return x;
        }
        bool operator==(const iterator& q) {
            return index == q.index;
        }
        bool operator!=(const iterator& q) {
            return index != q.index;
        }
    };
    iterator begin(){ return iterator(*this); }
    iterator end(){ return iterator(*this, sz); }

    DArray(unsigned n=1):cap(n),sz(n) {
        r = new T[n];
    }
    DArray(const DArray& a) {
        cap = a.cap; sz = a.sz;
        r = new T[sz];
        for(unsigned i; i<sz; i++) r[i] = a.r[i];
    }
    DArray& operator=(const DArray& right) {
        if(this!=&right) {
            delete [] r;
            cap = a.cap; sz = a.sz;
            r = new T[sz];
            for(unsigned i; i<sz; i++) r[i] = a.r[i];
        }
        return *this;
    }
    virtual ~DArray() { delete [] r; }

    T& operator[](int index) {
        if( index < 0 || index >= sz ) {
            throw IndexError( sz, index );
        }
        return r[index];
    }
    void ensureCapacity( unsigned newCap ) {
        if( newCap > cap ) {
            T *b = new T[newCap];
            for(unsigned i; i<sz; i++) b[i] = r[i];
            delete []r;
            r = b;
            cap = newCap;
        }
    }
    unsigned size() { return sz; }
    void add( T& e ) {
        if(sz == cap)
            ensureCapacity( 2+(unsigned)(1.1*cap));
        r[sz++] = e;
    }
    void removeFromPos( int pos ) {
        if( pos>=0 && pos<sz ) {
            for( unsigned i=pos-1; i<sz; i++ ) r[i-1] = r[i];
            sz--;
        }
    }
    int indexOf( T& e) {
        for(unsigned i; i<sz; i++)
            if( e == r.[i]) return i;
        return -1;
    }
    void insertAt( T& e, unsigned pos ) {
        if(sz == cap)
            ensureCapacity(2 +(unsigned)(1.1*cap));
        for(unsigned i=sz-1; i>=pos; i--) r[i+1] = r[i];
        r[pos] = e;
        sz++;
    }
    void forEach( void(*f)(T &)) {
        for(unsigned i=0; i<sz; i++) f(r[i]);
    }
};

template< class T> void print( T& x) {
    cout << x << endl;
}

int main() {
    int n;
    cin>> n;
    DArray<Tst> a(n);
    a.forEach( print<Tst>);
    cout << endl;
    DArray<Tst>::iterator p=a.begin();
    for(; p!=a.end(); p++ ) {
        cout << *p << endl;
    }
    return 0;
}