c++ 2d array pointer code example

Example 1: Pointer of 2D array

*(arr + i)  -  arr[i]  -  Base address of ith 1-D array -> Points to 0th element of ith 1-D array

Example 2: c++ smart pointer 2d array

#include <iostream>
#include <memory>
using namespace std;

int main(){
	//this just builds a 2D array pi that looks like
	//0 1 2 3 4
	//5 6 7 8 9
	//10 11 12 13
	//...	   24
	int** pi=new int*[5];
	
	//this counter is augmented by 5 in every loop,
	//for the value to be 0...,5,..10etc
	int counter=0;
	for(int j=0;j<5;j++){	
		int* i=new int[5];
		for(int j=0;j<5;j++)
			i[j]=j+counter;
		counter=counter+5;

		pi[j]=i;
		//just to print out the array
		for(int k=0;k<5;k++)
			cout<<pi[j][k]<<" ";
		cout<<endl;
	}
	cout<<endl;

	//trying the same thing using smart pointers
	unique_ptr<int*[]> smp_pi(new int*[5]);
	counter=0;	
	for(int j=0;j<5;j++){
		unique_ptr<int[]> smp_i(new int[5]);		
		for(int k=0;k<5;k++){
			smp_i[k]=counter+k;		
			cout<<smp_i[k]<<" ";
		}
		counter=counter+5;
		cout<<endl;
		smp_pi[j]=&smp_i[0];
		//smp_pi[j]=smp_i; //this does not compile. why?
	}
	cout<<endl;

	for(int j=0;j<5;j++){	
		for(int k=0;k<5;k++)
			cout<<smp_pi[j][k]<<" ";
		cout<<endl;
	}

	return 0;
}