“y a-t-il quelque chose comme le vecteur” Réponses codées

Y a-t-il quelque chose comme Vector x [100]

Whenever we declare a vector like:

	vector<int> v; 
Here, we do not specify the size of our vector. 
Whenever we just want to add an element we just push it into the vector
using the  v.push _ back(val)  function (where val is the value you want to 
push).

Suppose you haven't added any elements into the vector. 
Now, if you go on access any element position like  v[0]  or  v[7]  like one 
can when he declares an array, you will get a runtime error. Why?
Because vectors are dynamic in nature. Since, you haven't declared any size or 
pushed any element it's size is zero. So no element exists right now.

But if you declare it using:

vector<int> v(N); 
The compiler would there only create an dynamic array of
size N with all values initialized to zero. Now, you can randomly 
access elements but only from  v[0]  to  v[N−1] . But, if you want to 
add more than N elements then you can anytime use the push _ back()  
function to add elements.

Now, coming to

vector<int> v[N]; 
It creates a static array of N vectors of the first type i.e.  v[0]  
is now a whole new and different vector than v[1] which is totally different 
than  v[2]  and so on. If you want to push a value into the 1st vector 
that is  v[0] , you will do it by  v[0].push _ back(val) . 
To access that element you will call it by  v[0][0] (kind of a 2d matrix, 
isn't it?!). So, basically it is an array of initially empty vectors to
which you can add elements. These are very useful while you want to implement 
graphs where each node has it's own vector and the nodes to which it is joined 
are pushed into that particular node's vector.