有关下面C++代码的说法，正确的是（ ）。

1#include <iostream>2using namespace std;3 4class ManyData {5    int * __data;6    int head, tail, capacity;7public:8    ManyData(int cap) {9        capacity = cap;10        __data = new int[capacity];11        head = tail = 0;12    }13    void push(int val) {14        __data[tail++] = val;15    }16    int pop() {17        return __data[--tail];18    }19    int size() {20        return tail - head;21    }22};23int main() {24    auto myData = ManyData(100);25    myData.push(1);26    myData.push(2);27    myData.push(3);28    myData.push(100);29    cout << myData.size() << endl;30    cout << myData.pop() << endl;31    return 0;32}