Dont understand why I need this resize function for vector in C++

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C++

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I was reading some c++ code regarding binary functions and When i read the code, i didnt understand why there was a resize() function. Here is the code:

#include <vector>
#include <iostream>
using namespace std;
template <typename t="">
struct finddivision {
    T operator() (const int& val, const int& val2) {
        if (val > val2)
            cout << val / val2 << endl;
        else if (val2 > val)
            cout << val2/val << endl;
    }
};

int main() {
    vector<int> myvec1 {2, 4, 5,6, 7,2};
    vector<int> myvec2 {6, 16, 55, 36, 77, 22};
    vector<int> holdresult;
    holdresult.resize(myvec2.size());
    transform(myvec1.begin(), myvec1.end(), myvec2.begin(),holdresult.begin(), finddivision<int>());
}

The line where it says: holdresult.resize(myvec2.size()), doesnt make sense to me, because aren't vectors already dynamic and adjust to the size they are given?. Another thing is that, when i comment that line and run the program, i get this return statement:
Process finished with exit code 139 (interrupted by signal 11: SIGSEGV)

So my questions is:
- Why do i need to have that resize() function for my code to work?

What I have tried:

i tried searching for answers and articles regarding my problem, but nothing seemed to match up.