Check out example codes for "initialize vector of vector c++". It will help you in understanding the concepts better.

Code Example 1

#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;
}

Code Example 2

#include<bits/stdc++.h> 
using namespace std; 
  
int main(){ 
    int n = 3; 
    int m = 4; 
  
    // Create a vector containing n 
    //vectors of size m.  
    vector<vector<int> > vec( n , vector<int> (m, 0));  
  
    for (int i = 0; i < n; i++) { 
        for (int j = 0; j < m; j++){ 
            cout<< vec[i][j]<< " "; 
        } 
        cout<< "\n"; 
    } 
  
return 0; 
}

Code Example 3

// Initializing 2D vector "vect" with 
// values 
vector<vector<int> > vect{ { 1, 2, 3 }, 
                           { 4, 5, 6 }, 
                           { 7, 8, 9 } };

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