Pointer to Pointer - C++

    It really takes a bit of time to really understand and absorb the complexity of Pointers. No matter how much theoratical knowlege you gain about pointers, it will not help you fully understand it which is why you should code yourself and check each line and question yourself and your understanding. 

    Here I am simply adding a program that I coded to understand pointer to a pointer. I highly recommend that you actually type line by line in your own editer and run it step by step to really understand it. If I could summerize my understanding of a pointer in a few words, it would be "use pointer to a pointer when you want to change pointer's value outside of a function's scope". Please understand the code below by yourself to really know what I mean. 

Also added some helpful comments which can help you understand a bit faster, atleast that's my intention. Hope you find this helpful. Feel free to comment if you have any questions, I am happy to discuss and answer. 

 #include <stdio.h>
#include <iostream>

/*
Example to understand why we need a pointer to a pointer.
 
 */

using namespace std; 

void cant_change(int * x, int * z){
    x = z;
    cout << "cant_change() = Value of a inside cant_change function " << x << " and " << z << endl;
    cout << "cant_change() = Inside can't change function change will stay the same outside of this function scope?" << endl;

    cout << "can't change() = address of pointer a= " << &x << endl;
}

void change(int ** x, int * z){
    *x = z; 
    //dereferecing pointer to a pointer... **x = *x

    cout << "Change() = a's value inside change() a= " << *x  << " but because of pointer to pointer, this change should be take effect in main() too." << endl;
    cout << endl;
    cout << "Change() = address of pointer a= " << &*x << endl; 
    // &*x = address of pointer pointing to (*x) 

}

int main()
{

    int c = 1;
    int d = 2;
    int e = 3;

    int * a = &c;
    int * b = &d;
    int * f = &e;
    int ** pp = &a;  // pointer to pointer 'a'

    cout << "Main() = a' value= " << a << endl;
    cout << "Main() = b' value= " << b << endl;
    cout << "Main() = f' value= " << f << endl;

    cout << endl;

    cout << "Main() = a' address= " << &a << endl;
    cout << "Main() = b' address= " << &b << endl;
    cout << "Main() = f' address= " << &f << endl;
    
    cout << endl;
    
    cout << "Main() = c' address= " << &c << endl;
    cout << "Main() = d' address= " << &d << endl;
    cout << "Main() = e' address= " << &e << endl;

    cout << endl;
 
    cout << "Main() = Can we change a pointer? Let's see" << endl;
    cout << endl;
    cout << "Main() = operation performing a = b" << endl;
    cout << endl;
    a = b;
    cout << "Main() = a' value after a = b is =" << a << " = Same as b's value"  << endl;
    cout << endl;
    cout << "Main() = a and b dereference, a= " << *a << " and b=" << *b << endl;
    
    cout << endl;
    cout << "Main() = Can we perfom change in a function?" << endl;  
    
    cout << endl;
    cout << "Main() = Calling cant_change(a, f) function." << endl;

    cant_change(a, f);  // Passing pointers so can be regarded as *a, pass by value but for pointers
    //can think of this as *a, so duplicate values are stored in function scope.

    //lets print pointer's address so the picture can be clearer
    cout << endl;
    cout << "Main() = address of pointer a " << &a << endl; 
    
    cout << endl;
    cout << "Main() = value of a outside of can't cange function scope is " << a << endl;
    
    cout << endl;
    cout << "Main() = outside of cant_change function, a's value hasn't changed. it is same as a=b " << endl;

    cout << endl;
    cout << "Main() = Let's see if pointer to a pointer can help us with changing value outside of main() and still remain the same in Main() " << endl;

    change (&a, f); // passsing address of a pointer, pass by reference if you will, but for pointer.
    //can think of it as.... & of *a, so in function  change (int * (*a), *f);

    cout << endl;
    cout << "Main() = a value " << a << endl;

    //you don't need to pass address if you have double pointer already
    
    //pp is **p = &a; --- so below are the same.
    //change(pp, f);  is same as passing.... change(&a, f);
    //hope that clears up. 

    return 0;
}

Full code of this can be found here, file here can be updated or changed with addtional example. Pointer to Pointer full source code