1. Vectors
CSCE 121
J. Michael Moore

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

3. Array Really a pointer Variable name is a pointer to the first element
For ary[2]
Conceptually: address of ary + 2*sizeof(array datatype)
Actually: ary + 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

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

5. 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

6. 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

7. Multi-dimensional Vectors
A vector of vectors
vector< vector<int> > ary2d;
Access
ary2d.at(i).at(j) // safer
ary2d[i][j]