Vectors in C++

• Vectors

  • What they are
  • Advantages vs arrays
  • Declaration and initialization

• Suppose we want to store test scores for my school

• I have no way of knowing how many students will register next year

• Options:

  • Pick a size that you are not likely to exceed and use static arrays
  • Use a dynamic array such as vector

What is a vector?

• A vector is a sequence of elements that you can access by an index. It is a container in the C++ Standard Template Library (STL)
• An array that can grow and shrink in size at execution time
• Provides similar semantics and syntax as arrays
• Very efficient
• Can provide bounds checking
• Can use lots of functions like sort, reverse, find, and more.

Declaring

#include <vector>
using namespace std;

vector <char> vowels;
vector <int> test_scores;

// Using a constructor initialization syntax
vector <char> vowels(5);
vector <int> test_scores(10);

• Unlike arrays, the 10 integers will automatically be set to 0.

Initializing

vector <char> vowels {'a', 'e', 'i', 'o', 'u' };
vector <int> test_scores {100, 90, 88, 79, 93};
vector <double> hi_temperatures (365, 85.0); // (initial_size, initial_value)

Characteristics

• Dynamic size
• Elements are all the same type
• Stored contiguously in memory
• Individual elements can be accessed by their position or index
• First element is at index 0
• Last element is at index size-1
• [ ] - no checking to see if you are out of bounds
• Provides many useful function that do bounds check
• Elements initialized to zero
• Very efficient
• Iteration (looping) is often used to process