////////////////////////////////////////////////////////
//
//	liststrings.cpp
//
//	Started by Jeff Ondich on 5/27/98
//	Last modified 11/11/99
//
//	This program demonstrates pointers and linked
//	lists in C++ by considering linked lists of
//	characters.
//
////////////////////////////////////////////////////////

#include	<iostream>

// A struct is a class whose member data and functions
// are public by default.

struct CharNode
{
	char		mData;
	CharNode*	mNext; // An address of a CharNode
};


// It's convenient to have a type to represent
// a pointer to a node, in addition to the node
// type itself.

typedef 	CharNode *		CharNodePtr;



void ReadString( CharNodePtr& head );
void WriteString( CharNodePtr head );
void WriteStringBackwards( CharNodePtr head );


int main( void )
{
	// Initializing a pointer to 0 is how you
	// say "this linked list is empty now."

	CharNodePtr		message = 0;


	cout << "Type something, please: ";
	ReadString( message );

	cout << "You typed: ";
	WriteString( message );
	cout << endl;

	cout << "Backwards: ";
	WriteStringBackwards( message );
	cout << endl;

	return( 0 );
}


////////////////////////////////////////////////////////
//	ReadString reads a line of text from cin and
//	inserts it into a linked list whose first node is
//	pointed to by "head."
////////////////////////////////////////////////////////

void ReadString( CharNodePtr& head )
{
	char			c;
	CharNodePtr		newNode;
	CharNodePtr		previousNode;

	// If there's no string to read, make sure the
	// linked list is empty, and return.

	cin.get(c);
	if( !cin  ||  c == '\n' )
	{
		head = 0;
		return;
	}

	// If we've gotten to here, then we know there's at
	// least one character in the line, so we need to
	// create a node to put it in, and attach that
	// node to the front of the list.

	head = new CharNode;
	if( head == 0 )
	{
		cout << "Memory allocation trouble.  Bye." << endl;
		exit(0);
	}
	head->mData = c;
	head->mNext = 0;
	previousNode = head;


	// Now that we have a one-node list, we can do the
	// rest of the string in a loop.

	cin.get( c );

	while( c != '\n'  &&  !cin.fail() )
	{
		newNode = new CharNode;
		if( newNode == 0 )
		{
			cout << "Memory allocation trouble.  See you." << endl;
			exit(0);
		}
		newNode->mData = c;
		newNode->mNext = 0;
		previousNode->mNext = newNode;
		previousNode = newNode;
		
		cin.get( c );
	}
}


////////////////////////////////////////////////////////
//	WriteString writes the given string to cout.
//	Note that no endl is written.
////////////////////////////////////////////////////////

void WriteString( CharNodePtr head )
{
	CharNodePtr		current = head;
	
	while( current != 0 )
	{
		cout << current->mData;
		current = current->mNext;
	}
}


////////////////////////////////////////////////////////
//	WriteStringBackwards writes the given string
//	to cout, backwards.  Note that no endl is written.
////////////////////////////////////////////////////////

void WriteStringBackwards( CharNodePtr head )
{
	if( head != 0 )
	{
		WriteStringBackwards( head->mNext );
		cout << head->mData;
	}
}