Hi, I am having problems with my doubly linked list program. when I delete the last character in the list, it deletes the whole list - so I think i'm having a problem with my ptrs. Also, when I delete letters (other than the last one entered), it holds a different character in place of the letter that was entered to be deleted, and once the last letter entered is inputted to be deleted from the list, it outputs "the list is empty", even if not all the letters have been inputted to be deleted.
Here is my current code:
Code:#include <cstdlib> #include <iostream> #include <stdio.h> #include <stdlib.h> using namespace std; struct listNode { char data;//each listNode contains a character struct listNode *nextPtr; //pointer to 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, ListNodePtr *tPtr, char value ); char deletechar( ListNodePtr *sPtr, ListNodePtr *tPtr, char value); int isEmpty( ListNodePtr sPtr); void printList( ListNodePtr currentPtr ); void printBack( ListNodePtr currentPtr ); void instructions(void ); int main(int argc, char *argv[]) { ListNodePtr startPtr=NULL; /* initially there are no nodes */ ListNodePtr tailPtr=NULL; int choice; /* user's choice */ char item; /* char entered by user */ instructions(); /* display the menu */ printf("? "); scanf("%d", &choice); while(choice !=3){ switch(choice){ case 1: printf("Enter a character: "); scanf("\n%c", &item); insert(&startPtr, &tailPtr, item); /* insert item in list */ printList(startPtr); printBack(tailPtr); break; case 2: /* delete an element */ /* if list is no empty */ if(!isEmpty(startPtr)){ printf("Enter a character to be deleted: "); scanf("\n%c", &item); /* if character is found remove it */ if(deletechar(&startPtr, &tailPtr, item)){ /* remove item */ printf("%c deleted.\n", item); printList(startPtr); printBack(tailPtr); }/* 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; /* indicates successful termination */ }/* end main*/ 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 function instructions */ /* Insert a new value into the list in sorted order */ void insert( ListNodePtr *sPtr, ListNodePtr *tPtr, char value){ ListNodePtr newPtr; //pointer to new node ListNodePtr previousPtr; //pointer to previous node in list ListNodePtr currentPtr; //point to current node in list newPtr = (ListNodePtr)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 previousPtr=NULL; currentPtr=*sPtr; newPtr->prevPtr=NULL; //loop to find the correct location in the list while(currentPtr !=NULL&&value > currentPtr->data){ previousPtr=currentPtr; /* walk to ... */ currentPtr=currentPtr->nextPtr; /* ... next node*/ }//end while if(previousPtr==NULL){ // inserted at beginning of list newPtr->nextPtr=*sPtr; *sPtr=newPtr; *tPtr=newPtr; }//end if else{ //insert new node between previousPtr and currentPtr if(currentPtr!=NULL){ // inserted in the middle previousPtr->nextPtr=newPtr; newPtr->nextPtr=currentPtr; currentPtr->prevPtr=newPtr; newPtr->prevPtr=previousPtr; } else{//inserted at end of list *tPtr=newPtr; previousPtr->nextPtr=newPtr; newPtr->prevPtr=previousPtr; } } /* end else */ } /* end if */ else{ printf("%c not inserted. no memory available.\n", value); }//end else }//end function insert /* delete a list element */ char deletechar( ListNodePtr *sPtr, ListNodePtr *tPtr, char value){ ListNodePtr previousPtr; /* pointer to previous node in list */ ListNodePtr currentPtr; /* pointer to current node in list */ ListNodePtr tempPtr; /* temporary node pointer */ if( *sPtr == NULL ){//checks to see if list is empty return '\0'; } if((*sPtr)==(*tPtr)){//checks to see if start pointer and tail pointer are the same *tPtr=NULL; } /* delete first node */ if ( value == ( *sPtr )->data) {/* Begin if loop */ tempPtr = *sPtr; /* hold onto node being removed */ *sPtr = ( *sPtr )->nextPtr; /* de-thread the node */ *tPtr = ( *tPtr)->prevPtr; /* update prevPtr of new head of list */ free( tempPtr ); /* free the de-threaded node */ (*sPtr)->prevPtr = NULL; return value; } /* end if */ else { previousPtr = *sPtr; currentPtr = ( *sPtr )->nextPtr; /* loop to find the correct location in the 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; previousPtr->nextPtr=previousPtr; free( tempPtr ); return value; }/* end if */ } /* end else */ return '\0'; } /* end function delete */ /* Return 1 if the list is empty, 0 otherwise */ int isEmpty(ListNodePtr sPtr){ return sPtr==NULL; }/* end function isEmpty */ void printList(ListNodePtr currentPtr){ //if list is empty if(currentPtr==NULL){ printf("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"); } } void printBack(ListNodePtr currentPtr){ if(currentPtr==NULL){ printf("List is empty.\n\n"); } else{ printf("the list in reverse is:\n"); while(currentPtr !=NULL){ printf("%c --> ", currentPtr->data ); currentPtr=currentPtr->prevPtr; } printf("NULL\n\n"); } }
Originally Posted by pghpens91
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