C++ dynamic vector of pairs

Question

I need to dynamically allocate an array of 5 vectors of pairs . This code snippet is supposed to add first elements to all 5 vectors :

std::vector<std::pair<int, int>> * arr = new std::vector<std::pair<int, int>>[5];
for (int i = 0; i < 5; i++) {
    arr[i].push_back(std::make_pair(i+1, i+11));
}

But it adds only 1 element to arr[0] vector

for (auto el : *arr) {
    std::cout << el.first << ", " << el.second << std::endl;
}

Printing out gives 1, 11
What I need is

1, 11
2, 12
3, 13
4, 14
5, 15

Please give me some hints. How to work with dynamic vector of pairs?

EDIT: Vector of vectors is one possible way. However, I want to use an array of vectors.

Answer 1

Note : Edited entire answer because of the edit of the question.

---

The statement:

for (auto el : *arr) {
    std::cout << el.first << ", " << el.second << std::endl;
}

will print the element(s) for the first vector only (ie arr[0] ). That's because arr will decay as a pointer to the first element of the array.

---

If you want to print for all vector s , you need to iterate over the size of the array (as already done for the insertion):

for (int i = 0; i < 5; i++) {
    // arr[i] now is the i-th vector, and you can print whatever you want

    // For example the following will print all element for each vector.
    for (auto el : arr[i]) {
      std::cout << el.first << ", " << el.second << std::endl;
    }
}