Answer to Question #247470 in C++ for Angelie Suarez

Question

Simulate the fragment of codes below and trace the output. 

int *p1, *p2;

p1 = new int;

p2 = new int;

*p1 = 10;

*p2 = 20;

cout << *p1 << “ ” << *p2 << endl;

p1 = p2;

cout << *p1 << “ ” << *p2 << endl;

*p2 = 30;

cout << *p1 << “ ” << *p2 << endl;

Answer 1

#include <iostream>

using namespace std;
int main() {
 // defining 2 new pointers which points to nothing
 int *p1, *p2; 
 //new int : it allocate a new memory which can hold an object of type integer
 // p1 is now pointing to that newly allocated memory
 p1 = new int; 
 // same here, though p2 now points to another newly allocated memory
 p2 = new int; 
 //here the * dereference the pointer and accessing the value stored in the pointed memory
 // so here p1 points to a memory that stores a value of (int) 10
 *p1 = 10;
 // same here the * dereferences the pointer 
 // p2 now is pointing to a memory that store a value of (int) 10+10 = 20
 *p2 = *p1 + 10; 
 // at this line p2 will point to the same memory that p1 points to
 // so by dereferencing p1 or p2 they will give the same value
 //as they both point to the same memory and any change to the value stored in that memory
 //with either of them is the same
 // so p2 now points to a memory of stored value (int) 10
 p2 = p1;
 //at thise line p2 stored memory value is changed to be of value (int) 10 + 5 = 15
 // both p2 and p1  point to the same memory that have a stored value of (int) 15 
 *p2 = *p1 + 5; //15?
 // here it dereference both pointers to get the value stored in the memory
 cout << *p1 << " " << *p2 << endl; //??? 
 return 0;
}