declare 2d vector c++ with size code example

Example 1: how to make a 2d vector in c++

// Create a vector containing n 
//vectors of size m, all u=initialized with 0
vector<vector<int> > vec( n , vector<int> (m, 0));

Example 2: 2d vector

#include <bits/stdc++.h>
using namespace std;
int main() 
{
  int rows = 2;
  int cols = 2;
  int val = 1;
  vector< vector<int> > v(rows, vector<int> (cols, val));  /*creates 2d vector “v[rows][cols]” and initializes all elements to “val == 1” (default value is 0)*/
  v[0][0] = 5;
  v[1][1] = 4;
  cout << v[0][0] << endl; //Output: 5cout << v[1][0] << endl; //Output: 1return 0;}

Example 3: initialising 2d vector

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