c++11 - Can Someone explain this C++ code to me? -

its exemple of 2d pointers in 1 of slides teacher gave us. can't seem understand code other pointer pointer.

ps: still beginner @ c++

#include <iostream> using namespace std;  int **ptr; int main(){     ptr=new int *[3];     (int i=0;i<3;i++){         *(ptr+i)=new int[4];     }    for(int i=0;i<3;i++)        for(int j=0;j<4;j++){            *(*(ptr+i)+j)=i+j;            cout<<ptr[i][j];            cout<<"\n";        } return 0;  } 

taking account comments i'll try explain unclear.

let's assume there 3 integers

int x = 1; int y = 2; int z = 3; 

and going declare array of pointers these integers. declaration like

int * a[3] = { &x, &y, &z }; 

or

int * a[3];  *( + 0 ) = &x; // same a[0] = &x; *( + 1 ) = &y; // same a[1] = &y; *( + 2 ) = &z; // same a[2] = &z; 

take account array designator used in expressions rare exceptions converted pointer first element.

so example in expression

*( + 1 ) 

the array designator a converted pointer of type int **.

now if want same allocating array dynamically can write

int **ptr = new int *[3] { &x, &y, &z }; 

or

int **ptr = new int *[3];  *( ptr + 0 ) = &x; // same ptr[0] = &x; *( ptr + 1 ) = &y; // same ptr[1] = &y; *( ptr + 2 ) = &z; // same ptr[2] = &z; 

as type of pointer ptr int ** example expression ptr[0] has type int * , can store address of variable x in expression.

the expression ptr[0] having type int * equivalent expression *( ptr + 0 ) or *ptr.