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Q:

# how to get size of 2d vector in c++

``````#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;
}
``````
1
``````// Create a vector containing n
//vectors of size m, all u=initialized with 0
vector<vector<int> > vec( n , vector<int> (m, 0));  ``````
4
``````auto M = 4;	// num of rows
auto N = 3; // num of cols in each row
auto default_value = 1; // default value of all int elements
std::vector<std::vector<int>> matrix(M, std::vector<int>(N, default_value));``````
1
``````myVector[
Vector[0, 4, 2, 5],
Vector[1, 4, 2]
];

/*When you call for myVector[1].size() it would return 3 and [0] would return 4.

For the amount of rows (int vectors) in the 2d vector, you can just use myVector.size()

You can run this to see it in actions*/``````
2
``````// Initializing 2D vector "vect" with
// values
vector<vector<int> > vect{ { 1, 2, 3 },
{ 4, 5, 6 },
{ 7, 8, 9 } }; ``````
4
``````// finding size of a square matrix
myVector[0].size();``````
1