Why doesn't a pointer work if I initialize the pointer variables later?

Question

See my comment

Answer 1

Syntax for a single pointer declaration is :
<type> *<ptr_name> ;
Initialization is
< ptr_name > = <address of variable>;
Like ex :

int n = 5;
int *ptr;
ptr = &n;

You can combine like :
int *ptr = &n;
*ptr returns value;
ptr points to location;
so *ptr = &n ; is incompatibles.
int *ptr = &n ; is valid. // initialization at the time of declaration...
If you want reassign, use
ptr = &n; no * (dereference operator) .

note : pointer can hold address of another variable. this is it's purpose to use it.
ptr refers to address,
*ptr refers to value stored at the address.

Hope it helps..

Answer 2

// I declare and define pointer variable in a single line

#include <iostream>

using namespace std;

int main()

{

int value = 5;

int *firstP = &value;

int **secondP = &firstP;

int ***thirdP = &secondP;

cout << firstP << endl;

cout << secondP << endl;

cout << thirdP << endl;

cout << ***thirdP << endl;

return 0; }

it's working well

but if i initialize it later then the code doesn't work.

int value = 5;

int *firstP;

int **secondP;

int ***thirdP;

*firstP = &value;

**secondP = &firstP;

***thirdP = &secondP;

cout << firstP << endl;

cout << secondP << endl;

cout << thirdP << endl;

cout << ***thirdP << endl;

👆 In this case it is not working. Why?