initialise vector size c++ code example

Example 1: initialize vector of vector c++

#include <iostream>
#include <vector>
 
#define M 3
#define N 4
 
int main()
{
  // specify default value to fill the vector elements
  int default_value = 1;
  // first initialize a vector of ints with given default value
  std::vector<int> v(N, default_value);
  // Use above vector to initialize the two-dimensional vector
  std::vector<std::vector<int>> matrix(M, v);
  
  return 0;
}

Example 2: how to initialize vector in c++ with all elements 0

vector<int> arr(10,0);

Example 3: declare vector of size n in c++

#include <vector>

auto n = 20
// create a vector with n=20 integer elements
std::vector<int> arr(n);