Introduction to Pointers and Notes

1) Draw a diagram showing what happens in memory after each statement.

double *ptr1, ptr2;
double realNum = 1.234;
ptr1 = new double;
*ptr1 = 4.2;
ptr2 = ptr1;
*ptr2 = -4.09;	
if (*ptr1 == 4.2) cout << "Unchanged";
   else cout < "Changed";
if ( ptr1 == ptr2) cout << "Equals";
   else cout << "Not Equal";
prt2 = NULL;
if (ptr1 != NULL)
   delete ptr1;
ptr1 = &realNum;

2) Write a function to interchange pointers p and r, so that after the function is performed p will point to the item to which r formerly pointed, and vice versa.

Reference C++ for You++, Litvin, pp.179-198:

struct node
   int info;

Creating new nodes
p = new node;

Deleting of nodes
delete p;

The best time to use the new procedure is when you have some information to store into a node, not before. Pointers may be declared in variable declarations, but do not point to any information until new. Likewise delete frees the memory location, and does require a new declaration for use again.

3) Draw a diagram showing the situation in memory after execution of each of the statements in the following program that performs a series of demonstrations.

#include <iostream.h>
#include "apstring.h"
struct node
   apstring info;
   node *next;
int main( )
   node *A, *B;
   A = new node;
   B = new node;
   B -> info = "Sosa";
   B -> next = NULL;
   A -> info = "McGwire";
   A -> next = B;
   cout << A->next->info;
   delete B;
   delete A;
   return 0;

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