A vector is a dynamic array class implemented in the standard C++ library. This vector class has the ability to dynamically grow and shrink. The elements are placed in a contiguous fashion so that they can be traversed by iterators.
The very first step in using vectors is to learn how to declare and initialize them; there are four ways of initializing a vector in C++:
All the elements that need to populate a vector can be pushed, one-by-one, into the vector using the vector class method push_back. The push-back method is shown in the code below:
#include <iostream>#include <vector>using namespace std;int main() {vector<int> vec;vec.push_back(1);vec.push_back(2);vec.push_back(3);vec.push_back(4);vec.push_back(5);for (int i = 0; i < vec.size(); i++){cout << vec[i] << " ";}return 0;}
This method is mainly used when a vector is to be populated with multiple elements of the same value (e.g., if a vector needs to be populated with ten 1s). Take a look at the code below:
#include <iostream>#include <vector>using namespace std;int main() {int num_of_ele = 10;// the overloaded constructor takes the number of// values and the value itself as parameters.vector<int> vec(num_of_ele, 1);for (int i = 0; i < vec.size(); i++){cout << vec[i] << " ";}return 0;}
This method passes an array to the constructor of the vector class. The array contains the elements which will populate the vector. This method is shown in the code below:
#include <iostream>#include <vector>using namespace std;int main() {vector<int> vec{1,2,3,4,5};for (int i = 0; i < vec.size(); i++){cout << vec[i] << " ";}return 0;}
This method passes the begin() and end() iterators of an already initialized vector to a vector class constructor; a new vector is then initialized and populated by the elements in the old vector. Take a look at the code below:
#include <iostream>#include <vector>using namespace std;int main() {vector<int> vec_1{1,2,3,4,5};vector<int> vec_2(vec_1.begin(), vec_1.end());for (int i = 0; i < vec_2.size(); i++){cout << vec_2[i] << " ";}return 0;}
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