Is it possible to increment vector object in a loop ?

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I have to make several subvectors with lengths following elements of another vector
For example :

vector<int> A{2,3}
// Vector A has 2 elements, therefore I need to make 2 subvectors

A[0] = 2, make a new subvector with length of 2, example : B {11,12}	
A[1] = 3, make a new subvector with length of 3, example : C {13,14,15}

With vector of vector, I need to fill the inner vector first (subvectors) and pass it to the outer vector. However, in my case I need to fill the outer vector first, and make subvectors based on that : how many elements it has (to be used as number of subvectors) and the value of each elements (to be used as the size of each subvectors).

What I have tried:

I tried to initialize subvectors inside of a loop, however I don't know how to increment it.

int data = 0;
vector<int> A{2,3}; --> // An example, in the actual implementation this vector size is unkwown and elements are filled using cin.

for (int i = 0; i < A.size(); i++){
	vector<int> B(A[i]); 
    //a subvector with size of A[i]
    //is it possible to increment this object ?
				
	for (int j = 0; j < A[i]; j++){
		cin >> data;
		B.push_back(data); //need to push the next i iteration to a new subvector
	}	
}

Posted 21-Feb-22 23:44pm

lock&_lock

Updated 21-Feb-22 23:58pm

v4

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CPallini · Accepted Answer · 2022-02-21T23:58:00

You need a containers for your subvectors. You might, for instance, use a vector of vectors:

#include <iostream>
#include <vector>
using namespace std;

int main()
{

  vector<int> v{2,3};
  vector < vector < int > > sv; // the sub-vectors

  for (size_t i = 0; i < v.size(); ++i)
  {
    sv.push_back(vector<int>{});
    for (int j = 0; j < v[i]; ++j)
    {
      sv[i].push_back(rand()); // just for testing, random initialization
    }
  }


  for (size_t i = 0; i < v.size(); ++i)
  {
    for (size_t j = 0; j < sv[i].size(); ++j)
      cout << sv[i][j] << " ";
    cout << endl;
  }

}