std::vector not working in for each loops code example

Example 1: how to iterate trough a vector in c++

vector<int> myVector;

myVector.push_back(1);
myVector.push_back(2);
myVector.push_back(3);
myVector.push_back(4);

for(auto x: myVector){
	cout<< x << " ";

}

vector<pair<int,int>> myVectorOfPairs;

myVectorOfPairs.push_back({1,2});
myVectorOfPairs.push_back({3,4});
myVectorOfPairs.push_back({5,6});
myVectorOfPairs.push_back({7,8});

for(auto x: myVectorOfPairs){
	cout<< x.first << " " << x.second << endl;

}

Example 2: c++ looping through a vector

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

Example 3: c++ looping through a vector

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