PLEASE EXPLAIN HOW DOES THE DELETE FUNCTON WORKS N THS CODE (USE MOCROSOFT WORD AND DRAW THE MAP OF THE POTERS WHCH PONTS TO WHCH )

/* Fig. 12.3: fig12_03.c Operating and maintaining a list */ #include #include

/* self-referential structure */ struct listNode { char data; /* each listNode contains a character */ struct listNode *nextPtr; /* pointer to next 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 );

int main( void ) { ListNodePtr startPtr = NULL; /* initially there are no nodes */ int choice; /* user's 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( " %c", &item ); insert( &startPtr, item ); /* insert item in list */ printList( startPtr ); break;

case 2: /* delete an element */

/* if list is not empty */ if ( !isEmpty( startPtr ) ) { printf( "Enter character to be deleted: " ); scanf( " %c", &item );

/* if character is found, remove it*/ if ( delete( &startPtr, item ) ) { /* remove item */ printf( "%c deleted. ", item ); printList( startPtr ); } /* end if */ else { printf( "%c not found. ", item ); } /* end else */ } /* end if */ else { printf( "List is empty. " ); } /* end else */

break;

default: printf( "Invalid choice. " ); instructions(); break; } /* end switch */

printf( "? " ); scanf( "%d", &choice ); } /* end while */

printf( "End of run. " ); return 0; /* indicates successful termination */ } /* end main */

/* display program instructions to user */ void instructions( void ) { printf( "Enter your choice: " " 1 to insert an element into the list. " " 2 to delete an element from the list. " " 3 to end. " ); } /* end function instructions */

/* Insert a new value into the list in sorted order */ void insert( ListNodePtr *sPtr, char value ) { ListNodePtr newPtr; /* pointer to new node */ ListNodePtr previousPtr; /* pointer to previous node in list */ ListNodePtr currentPtr; /* pointer to current node in 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 */

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 */ } /* end while */

/* insert new node at beginning of list */ if ( previousPtr == NULL ) { newPtr->nextPtr = *sPtr; *sPtr = newPtr; } /* end if */ else { /* insert new node between previousPtr and currentPtr */ previousPtr->nextPtr = newPtr; newPtr->nextPtr = currentPtr; } /* end else */ } /* end if */ else { printf( "%c not inserted. No memory available. ", value ); } /* end else */ } /* end function insert */ /* Delete a list element */ char delete( ListNodePtr *sPtr, char value ) { ListNodePtr previousPtr; /* pointer to previous node in list */ ListNodePtr currentPtr; /* pointer to current node in list */ ListNodePtr tempPtr; /* temporary 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 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; 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 */ /* Print the list */ void printList( ListNodePtr currentPtr ) { /* if list is empty */ if ( currentPtr == NULL ) { printf( "List is empty. " ); } /* end if */ else { printf( "The list is: " ); /* while not the end of the list */ while ( currentPtr != NULL ) { printf( "%c --> ", currentPtr->data ); currentPtr = currentPtr->nextPtr; } /* end while */ printf( "NULL " ); } /* end else */

} /* end function printList */