//This is our third simple C++ program

#include <iostream>
using namespace std; 

int main(){

// Pointer Example

   int i = 10; //an initialized int, will be automatically allocated
   cout << endl << "i is an automatic var allocated at addr:" << &i << endl << endl;
 
   int *ptr_to_i = &i; //initialize ptr_to_i with the address of i 
   int *pi;   //unititialized pointer to int
   int **ppi; //uninitialized pointer to pointer to int 
 
   cout << "ptr_to_i is an automatic pointer to int variable." << " ptr_to_i has been allocated at addr:" << &ptr_to_i << endl << " and the value of ptr_to_i is:" << ptr_to_i << " which is the same as addr of i:" << &i << endl << endl;

   ppi = &ptr_to_i; //put the address of ptr_to_i into ppi //LINE 7 !!!

                                     
   pi = *ppi;    // same as pi = ptr_to_i;
		 // * is the "follow-the-pointer-arrow and evaluate that 
		 //location" operator. ppi points to ptr_to_i. following the
		 //arrow once gives us ptr_to_i

   cout << "*ppi = " << **ppi << endl; 
                  //Following the ppi pointer once gives us ptr_to_i
	          //as above. Following ptr_to_i once after that gives us i;
   return 0;
}


//The picture might make things clearer:

//         ___________                  ___________            ___________
//   ppi  |___________|------> ptr_to_i|___________|------>   |_____ 10 __|
//       (p. to p. to int)             (pointer to int)       (int)     
//                                                                    ^
//                                                                    |
//                                                                    |
//                               ___________                          |
//                           pi |___________|-------------------------|
//                             (pointer to int)
 


Then type the following
command at the command prompt:

g++ -o pointers pointers.cc

Then type at the command prompt
pointers 
to execute your program.

Try to reason about the output you get in each case and why you get it.
If you don't understand an output, please ask me about it. Pointers
are hard to understand so don't be shy about this.

Comment line 7 above - i.e., use an unitialize pointer. You might get a 
SEGFAULT or BUS ERROR on the next line when trying to follow and unitialized
pointer **ppi (i.e., your program will crash). 

-Cristiana