array it needs a constant value
const int seq_size = 18;
int pell_seql[seql_size];
//defined a constant value: seq_size = 18
As vector，First, we need to include Head file of vector: #include<vector>
vector is a template，So we need to add curly braces <Type> Size don't need to be a Constant value here
#include<vector>
vector<int> pell_seql(seq_size);//Attention! Size don't need to be a constant value here
whether array or vector，we can appoint Location，by []
pell_seql[0] = 1;//The first element is 1
pell_seql[1] = 2;//The second element is 2
initialization
array
int elem_seq[seql_size] = {,,,};//cant over size
vector
First Merhod（Troublesome）
vector<int>elem_seq(seql_size);
elem_seq[0] = 1;
elem_seq[1] = 2;
............etc
The second Method
int elem_vals[seq_size] = {1,2,3,4,5,6,7,8,9};
vector<int>elem_seq(elem_vals,elem_vals + seq_size)//the two values here refer to location，They identify Initialized element range