迭代std :: vector(没有迭代器)时使用哪种类型？

#include<iostream>
#include<vector>

int main() {
    std::vector<int> vec = {1, 2, 3, 4, 5};

    for (size_t i = 0; i < vec.size(); ++i) {
        std::cout<< vec.at(i)<< std::endl;
    }

    return 0;
}

#include<iostream>
#include<vector>

int main() {
    std::vector<int> vec = {1, 2, 3, 4, 5};

    for (size_t i = 0; i < vec.size(); ++i) {
        std::cout<< vec[i]<< std::endl;
    }

    return 0;
}