The Vector Class

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• A Reference
• Vector is possibly the most useful container.
• It is a dynamic array
• Designed for situations where
  • You add and remove most of the data from the end of the array.
  • Sort once, search many.
  • But you don't necessarily know how much data you will have.
• It is expensive
  • To delete items from anywhere but the end.
• You need to include vector

  #include < vector> 

• It is part of the standard namespace, so either

• // do this
  using namespace std;
  
  // or 
  std::vector<...>
  

• Definitely do the second in header files.
• To declare a vector

  • vector<int> numbers;
    vector<string> words(10); // declare a vector of 10 strings
    vector<float> values(15, 1.0); // declare a vector with 15 floats initialized to 1.0 

  • See the constructor reference
    • Omitting the size creates an empty vector
    • Omitting the initial value creates an vector of 0, 0.0, nullptr.
  • Vectors can be initialized in two other ways.
    • initializer-list

      vector <int> myNumbers({1,2,3,4,5}); 

    • A uniform initialization

      vector <int> myNumbers = {1,2,3,4,5} ; 

• Data Access
  • [] is access without bounds checking.
  • .at(size_t) is access with bounds checking.
  • .front() returns the element at position 0, not as useful
  • .back() returns the element at the last position, more useful.
  • .data() returns a pointer to the actual array.
• Size related
  • .size() returns the size of the vector.
• Adding/removing elements to the vector
  • .push_back(item) increases the size by 1 and adds the element at the end.
  • .pop_back() removes the last item from the vector.
• The comparison operators work on vectors.
  • Pairwise comparison
  • But only if the elements in the vector have that operation.
• simpleVector.cpp demonstrates much of this.
• The assignment operator is overloaded for vectors.
• Write a program that generates n random numbers and prints them out in the order generated and in reverse order generated.