Vectors CSCE 121

Group of homogeneous elements accessed by an index. Array/Vector Group of homogeneous elements accessed by an index. Vector access with arr.at(index) Bounds checking Array and Vector access with arr[index] No bounds checking

Array Really a pointer Variable name is a pointer to the first element For arr[2] Conceptually: address of arr + 2*sizeof(array datatype) Actually: arr + 2 (math is done automatically) Pointer arithmetic Must know size of array at compile time Allows access to elements outside of array bounds Security problem

Vector Abstraction (An array on the heap.) Preferred over arrays If you use .at() Bounds checking Prevents access outside array bounds Resizable #include <vector>

Vector Must say what type it is e.g. vector<int> Define size at beginning vector<int> vec = vector<int>(SIZE); vector<int> vec = vector<int>(SIZE,INIT_VAL); Let vector grow as needed vector<int> vec; vec.push_back(7); Increases size by one

Vector vector<int> vec; vec.push_back(7); vec.erase(vec.begin()+index); vec.at(index); // range checking & harder to read vec[index]; // no range checking & easier to read

Multi-dimensional Vectors A vector of vectors vector< vector<int> > arr2d; Access arr2d.at(i).at(j) // safer arr2d[i][j]