Modify to make Doubly Linked List

This is a discussion on Modify to make Doubly Linked List within the C Programming forums, part of the General Programming Boards category; .......

  1. #1
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    ....
    Last edited by Dampecram; 10-29-2008 at 11:22 AM.

  2. #2
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    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    /* self referential structure */
    struct listNode {
    	char data; /* each listNode contains a character */
    	struct listNode *nextPtr; /* pointer to the next node */
    	struct listNode *prevPtr; /* pointer to previous node */
    }; /* end structure listNode */
    
    typedef struct listNode ListNode; /* synonym for struct listNode */
    typedef ListNode *ListNodePtr; /* synonym for ListNode* */
    
    /* prototypes */
    void insert( ListNodePtr *sPtr, char value );
    char delete( ListNodePtr *sPtr, char value );
    int isEmpty( ListNodePtr sPtr );
    void printList( ListNodePtr currentPtr );
    void instructions( void );
    void printBackwards (ListNodePtr currentPtr );
    
    int main()
    {
    	ListNodePtr startPtr = NULL; /* initially there are no nodes */
    	int choice; /* users choice */
    	char item; /* char entered by user */
    	
    	instructions(); /* display the menu */
    	printf( "? " );
    	scanf( "%d", &choice );
    	/* loop while user does not choose 3 */
    	while ( choice != 3 ) {
    		switch ( choice )
                    {
    		    case 1 :
    			printf( "Enter a character: ");
    			scanf( "\n%c", &item );
    			insert( &startPtr, item ); /* insert item in the list */
    			printList( startPtr );
    			printBackwards( startPtr );
    			break;
    		    case 2:
    			/* if list is not empty */
                		if (!isEmpty(startPtr )) {
    				printf( "Enter character to be deleted: ");
    				scanf( "\n%c",&item); 
    				/* if character is found remove it */
    				if (delete( &startPtr, item ) ) {
                        			printf( "%c deleted.\n", item);
    					printList( startPtr );
    					printBackwards( startPtr );
    				} /* end if*/
    				else {
    					printf( " %c not found.\n\n", item);
    				} /* end else */
    			} /* end if */
    			else {
    				printf( "List is empty.\n\n" );
    			} /* end else */
    			break;
    		    default:
    			printf( "Invalid choice.\n\n" );
    			instructions();
    			break;
    		} /* end switch */
    		printf("? ");
    		scanf( "%d", &choice );
    	} /* end while */
    	printf( "end of run.\n" );
    	return 0; /* indicate sucessful termination */
    } /* end main */
    
    /* display program instructions to user */
    void instructions ( void )
    {
    	printf( "Enter your choice:\n"
    		"   1 to insert an element into the list.\n"
    		"   2 to delete an element from the list.\n"
    		"   3 to end.\n" );
    } /* end of instructions */
    
    /* insert a new value into the list in sorted order */
    void insert ( ListNodePtr *sPtr, char value)
    {
    	ListNodePtr newPtr;       /* pointer to a new node */
            ListNodePtr previousPtr;  /* pointer to previous node in list */
            ListNodePtr currentPtr;  /* pointer to current node on list */
    	newPtr = malloc( sizeof( ListNode )); /* create node */
    	if ( newPtr != NULL ) { /* is space available */
    		newPtr->data = value; /*place value in node */
    		newPtr->nextPtr = NULL; /*node does not link to another node */
    		newPtr->prevPtr = NULL;
    		previousPtr = NULL;
    		currentPtr = *sPtr;
    
    		/* loop to find the correct location in the list */
    		while (currentPtr != NULL && value > currentPtr->data) {
                		previousPtr = currentPtr;          /* walk to........*/
    			currentPtr = currentPtr->nextPtr;  /* .....next node */
    
    		        /* add here , point up stream */
    		} /* end while */
    
    		/* insert new node at begining of list */
    		if ( previousPtr == NULL ) {
    			newPtr->nextPtr = *sPtr;
    			
                    	if(*sPtr != NULL)
                        	    (*sPtr)->prevPtr = newPtr;
                  
                    	*sPtr = newPtr;
    		} /* end if */
    		else { /* insert new node between previousPtr and currentPtr */
    			newPtr->prevPtr = previousPtr;
                		previousPtr->nextPtr = newPtr;
    			newPtr->nextPtr = currentPtr;
                            if (currentPtr != NULL)
                                currentPtr->prevPtr = newPtr;
    			
    		} /* end else */
    	} /* end if */
    	else {
    		printf( "%c not inserted. No memory available.\n", value );
    	} /* end else */
    } /* end function insert */
    
    /* delete a list element */
    char delete ( ListNodePtr *sPtr, char value )
    {
    	ListNodePtr previousPtr; /* pointer to previous node on list */
            ListNodePtr currentPtr;  /* pointer to current node on list */
            ListNodePtr tempPtr;     /* temperary node pointer */
    	/* delete first node */
    	if (value == ( *sPtr )->data) {
    		tempPtr = *sPtr; /* hold onto node being removed */
    		*sPtr = ( *sPtr )->nextPtr; /* de-thread the node */
    		free( tempPtr ); /* free the de-threaded node */
    		return value;
    	} /* end if */
    	else {
    		previousPtr = *sPtr;
    		currentPtr = ( *sPtr )->nextPtr;
    		/* loop to find correct location on list */
    		while ( currentPtr != NULL && currentPtr->data != value )  {
    			previousPtr = currentPtr;            /* walk to ....*/
    			currentPtr = currentPtr->nextPtr;    /*....next node*/
    		} /* end while */
    		/* delete node at currentPtr */
    		if ( currentPtr != NULL ) {
    			tempPtr = currentPtr;
    			previousPtr->nextPtr = currentPtr->nextPtr;
    			free ( tempPtr );
    			return value;
    		} /* end if */
    	} /* end else */
    	return '\0';
    } /* end function delete */
    
    /* return 1 if list is empty, 0 otherwise */
    int isEmpty ( ListNodePtr sPtr )
    {
    	return sPtr == NULL;
    } /* end function isEmpty */
    
    /* Print the list */
    void printList ( ListNodePtr currentPtr )
    {
    	/* if list is empty */
    	if ( currentPtr == NULL) {
    		printf( " The list is empty.\n\n" );
    	} /* end if */
    	else {
    		printf( " The list is:\n" );
    		/* while not the end of the list */
    		while ( currentPtr != NULL ) {
    			printf( "%c --> ", currentPtr->data );
    			currentPtr = currentPtr->nextPtr;
    		} /* end while */
    		printf( "NULL\n\n" );
    	}/* end else */
    	
    } /* end function printlist */
    
    void printBackwards ( ListNodePtr currentPtr )
    {
         ListNodePtr temp = NULL;
     
    	  while ( currentPtr != NULL ) {
    		 temp = currentPtr;
    		 currentPtr = currentPtr->nextPtr;
    		 
    		 }
    		 
          printf( "\nThe list in reverse is:\n" );
          printf( "NULL" );
     
    		 currentPtr = temp;
    		 while ( currentPtr !=  NULL) {
    		 printf( " <-- %c", currentPtr->data );
    		 currentPtr = currentPtr->prevPtr;
    		 }
    		 
    		 printf("\n\n");
    		 
    }

  3. #3
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    wow thank you so much. This topic in C has been driving me crazy.. Ive been stumped on that part for a while.. Thanks a lot, now thats one less thing to worry about, now its time to work on the delete function, heh

    thank you again

  4. #4
    Registered User whiteflags's Avatar
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    Why did you remove your original question, now no one else knows for sure what this was about.

  5. #5
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    I agree with citizen you should not have removed your original post. You might want to repost your question for the sake of everyone.

  6. #6
    Algorithm Dissector iMalc's Avatar
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    I'm not a fan of playing Jeopardy either.

    Next time we'll either quote your entire post to reply, or we simply wont answer at all.
    My homepage
    Advice: Take only as directed - If symptoms persist, please see your debugger

    Linus Torvalds: "But it clearly is the only right way. The fact that everybody else does it some other way only means that they are wrong"

  7. #7
    Banned master5001's Avatar
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    If I wanted to take a stab at "why" my guess would be that the teacher wonders through the forums periodically. But who knows.

  8. #8
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    My original problem was that I was missing part of the link in the program for prevPtr. When I ran the program, the print forward would work fine, but the print backwards wasn't working correctly. I was losing part of my list in my insert function and couldn't figure out why. For example.. When I entered the word dog.. when my program would display.. the "g" would be lost when printed in reverse and that showed my prevPtr had something wrong with it.

  9. #9
    Algorithm Dissector iMalc's Avatar
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    Okay cool. Thanks for coming back to put that back in.
    My homepage
    Advice: Take only as directed - If symptoms persist, please see your debugger

    Linus Torvalds: "But it clearly is the only right way. The fact that everybody else does it some other way only means that they are wrong"

  10. #10
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    i have a question, the double link list right, i was told it points to both the previous and the next nodes but i dont fully understand how they work and also the circular link list.

  11. #11
    Banned master5001's Avatar
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    I use circular linked lists for memory management frequently. The proven advantage of circular linked lists is it very easy to insert elements without having any sort of "special case"

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