C++ to allocate memory to the two dimensional pointer of of implementation code

The principle is not written here, after all, there are a lot of online introduction, the code is as follows:

#include <iostream>
using namespace std;
#define  N  5
#define  M  10
int main(int argc, char **argv)
{
 int **p;
 int i,j;
 p = new int* [N];
 for (i = 0; i < N; i++)
  p[i] = new int [M];
 for (i = 0; i < N; i++)
  for (j = 0; j < M; j++)
   p[i][j] = i + j;
 for (i = 0; i < N; i++)
 {
  for (j = 0; j < M; j++)
  { 
   cout<<"["<<p[i][j]<<"]"<<"  ";
   cout<<*(*(p + i) + j)<<" "<<endl;
  }
  cout<<endl;
 }
 for (i = 0; i < N; i++)
 {
  delete [] p[i];
  p[i] = NULL;
 }

 delete [] p;
 p = NULL;
 return 0;
}