how to iterate over a vector in C++ code example

Example 1: c++ iterate through vectgor

std::vector<int> vec_of_ints(100);
for (int i = 0; i < vec_of_ints.size(); i++){
 	std::cout << vec_of_ints.at(i) << " "; 
}
std::cout << std::endl;

Example 2: c++ iterate over vector

for(auto const& value: a) {
     /* std::cout << value; ... */
}

Example 3: c++ looping through a vector

for(std::vector<T>::size_type i = 0; i != v.size(); i++) {
    v[i].doSomething();
}

Example 4: c++ looping through a vector

vector<int> vi;
...
for(int i : vi) 
  cout << "i = " << i << endl;