Chapter 6: Vectors¶
CSE 2010 Week 9¶
Arrays walked so that Vectors could run¶
● Arrays are all fine and dandy, but one big limitation to them is that they cannot¶
change in size once they have been defined. There might be times when we¶
want to dynamically allocate memory and change the size of the container. This¶
is where vectors come in.¶
● Definition:¶
○ Vectors are dynamically allocated arrays provided by the C++ Standard Template Library (STL).
○ They are data structures that store an indexed sequence of elements of the same data type, and
can change in size.
● To use vectors, we must¶
○ #include \
Declaring and¶
Initializing Vectors¶
● vector<datatype> vectorName;
○ Creates an empty vector. No mem allocated.
Example: vector<int> x;
● vector<datatype> vectorName(n);
○ Creates a vector of n elements, all with a default value
Example: vector<int> y(3);
● vector<datatype> vectorName(n, default value);
○ Creates a vector of n elements, with specified value
Example: vector<int> z(4,100);
● vector<datatype> vectorName{element1, element2...element n};
○ Creates a vector with n elements
Example: vector<int> w{3,20,8};
Vector Functions¶
● The vector class includes many member functions that allow us to modify or get¶
information about a vector (similar to the string class).¶
● Syntax for using vector member functions:¶
vectorName.functionName(); //must invoke with an existing vector¶
● Adding/deleting elements:¶
○ push_back(n) : appends the value n to the end of a vector¶
vector<int> x; //x is empty
x.push_back(4); // x = 4
x.push_back(6); // x = 4, 6
○ pop_back(); deletes the last element in a vector¶
vector<int> y{5,6,7}; // y = 5,6,
y.pop_back(); // y = 5,
● Vectors are considered last in, first out data structures. So when you add or delete elements, it¶
does so through the end of the vector.¶
Vector Functions¶
● Other helpful functions¶
● size(): returns the size of a vector¶
○ Because vectors are dynamically allocated and their size can change, you can add or delete as many elements
as you want. To find out the actual size of a vector you can use .size() (similar to .length() for string)
● clear(): clears the vector of all elements, setting its size to 0¶
● empty(): // returns true if the vector has a size of 0, returns false otherwise¶
Visit : http://www.cplusplus.com/reference/vector/vector/ For a full list of vector member functions and more information on vectors
Printing Vector Elements (printVector.cpp)¶
● Like arrays, we can access specific vector
elements with the [ ] operator by
providing an index #.
● We could use this method or a range
based for loop to print vector elements.
Output:
Modifying Vector Elements (changeVector.cpp)¶
Vectors in Functions¶
● Just like arrays, we can have vectors as parameters.
● Unlike arrays, vectors are passed by value. Meaning an identical copy of that vector is created in the scope of the
function.
● This can be very time and resource consuming, so whenever possible, pass your vectors by reference.
Example:
void fillVector(vector\