为什么在C ++中输入数组时不能输入向量？

Question

The wiki says:
The elements of a vector are stored contiguously. AND
Vectors allow random access; that is, an element of a vector may be referenced in the same manner as elements of arrays (by array indices).

So why can't we input the elements of a vector as:

vector<int> v;
for(int i=0;i<3;i++)
{
    cin>>v[i];
}

Answer 1

Either you need to resize the vector upfront - as other answers say - or you can use C++ standard library. Then the equivalent of your for loop is the following one line:

copy_n(istream_iterator<int>(cin), 3, back_inserter(v));

and it takes care of allocation/resizing.

Answer 2

The problem is that you need to allocate the elements of the vector first. So try vector<int> v(4); , so it will start with 4 elements. Then you can load values into them.

Answer 3

Your vector has zero elements right now. Try allocating it some space as:

vector<int> v(5);

Then your method would work.