c 2b 2b code to write 2d array

1#include <iostream>
2using namespace std;
3int main(){
4	int n,m;
5	int a[n][m];
6	cin >> n >>m;
7	for ( int i=0; i<n; i++){
8		for (int j=0; j<m; j++){
9			cin >> a[i][j];
10		}
11	}
12	
13	for ( int x=0; x<n; x++){
14		for (int y=0; y<m; y++){
15			cout << "a[" << x << "][" << y << "]: ";
16			cout << a[x][y] << endl;
17		}
18	}
19	return 0;
20}