Hello, I get the following seg fault error when I try to delete the last node of the list. Does anyone know why? My delete function and high level function are included below: The seg fault only occurs when the if value in BeginQuizFirstTry detecting that CheckAnswer is not true or = 0. Can anyone tell me why this seg faults?
int Delete (NODEPTR *headPtr, char *target)
{
/* Node pointers that reference the previous node
and the current node in the list. */
NODEPTR prev = NULL, curr = NULL;
/* Check to see if the list is empty. */
if (IsEmpty (*headPtr))
{
/* Display an appropriate message indicating that
deleting from the list was not accomplished
because the list is empty. */
fprintf (stderr, "Unable to delete from an empty list.\n\n");
/* If the list is empty, return the integer value
of -1, indicating that the question, char
*target, was not successfully deleted from the
list. */
return (-1);
}
/* Traverse the list until the target value is found. */
else
{
/* Initialize the node pointer referencing a previous
node in the list to NULL. */
prev = NULL;
/* Set the node pointer referencing a current node to
the head of the list. */
curr = *headPtr;
/* First check to see if the question, char *target,
that we want to delete is stored in the first
node in the list, because this would require
*headPtr to be modified. */
if (strcmp ((*headPtr) -> data.question, target) == 0)
{
/* If the question, char *target, is stored in the
first node in the list, change the head of the
list to start at the node pointer referencing
the current node's next pointer. */
*headPtr = curr -> next;
/* Delete and free the memory that was being used
to store the question, char *target, in the
first node of the list. */
free (curr);
/* If the question, char *target, was freed and
deleted, return the integer value of 1,
indicating that the question was successfully
deleted from the list. */
return (1);
}
/* Otherwise, traverse through the list to find the
question, char *target, to be deleted. */
else
{
/* Traverse the list if the node pointer
referencing the current node in the list is not
equal to NULL and the node pointer referencing
the current node in the list is not storing the
question, char *target, in the data portion of
its node. */
while ((curr != NULL) &&
(strcmp (curr -> data.question, target) != 0))
{
/* Traverse the list. */
prev = curr;
curr = curr -> next;
}
/* If the node pointer refencing the current node in
the list not equal to NULL, then the question,
char *target, was found. */
if (curr != NULL)
{
/* Change the next pointer of the previous node,
in order to avoid a broken list. */
prev -> next = curr -> next;
/* Delete and free the memory that was being used
to store the question, char *target, in this
node of the list. */
free (curr);
/* If the question, char *target, was freed and
deleted, return the integer value of 1,
indicating that the question was successfully
deleted from the list. */
return (1);
}
/* Otherwise, the question, char *target, was not
found in the list. */
else
{
/* If the question, char *target, was not found
in the list, return the integer value of -1,
indicating that the question was not
successfully deleted from the list. */
return (-1);
}
}
}
}
int BeginQuizFirstTry (NODEPTR *headListPtr1,
NODEPTR *headListPtr2,
int numberOfTotalQuestions)
{
/* A node pointer that will reference the current node
in the list, starting with the head pointer of the
first list. */
NODEPTR curr = *headListPtr1;
/* A node pointer that will reference a temporary node
in the list, which will be used for inserting nodes
into the second list. */
NODEPTR temp;
/* An array of characters, or a string, which will hold
the answer that the user inputted for the given
question that he/she was being asked during the quiz. */
char questionAnswer [NUMBEROFANSWERCHARACTERS];
/* An integer counter variable that will be used to
label each of the questions in the quiz. */
int questionCounter = 0;
/* An integer counter variable that will be used to
count the number of questions that the user answered
correctly during his/her trial of taking the quiz. */
int correctAnswerCounter = 0;
/* A QUIZ structure that will be used to insert each
question from the first list, into the second list. */
QUIZ insertedQuestion;
/* A float variable that will be used to store the
user's percentage of correct answers during the
user's first trial of taking the quiz. */
float scoreTrial1;
/* Display a message indicating that the quiz has
begun for the user. */
printf ("Here are your questions. Good luck !!!\n\n");
/* Traverse the list until the end. */
while (curr != NULL)
{
/* Increment questionCounter each time a new question
from the quiz is presented to the user. */
questionCounter++;
/* Display each of the questions in the quiz to the
user. */
printf (" %d. ", questionCounter);
DisplayQuestion (curr);
/* Read in the user's answer for each of the questions
in the quiz. */
scanf ("%s", questionAnswer);
/* If the user's answer is not correct, then delete it
from the first list and insert it into the second
list. */
if (CheckAnswer (curr, questionAnswer,
&correctAnswerCounter) != 1)
{
/* Copy the original question and correct answer that
the user was just being asked into the QUIZ structure,
insertedQuestion. */
strcpy (insertedQuestion.question, curr -> data.question);
strcpy (insertedQuestion.answer, curr -> data.answer);
/* Create enough space in memory for a temporary node
that will be inserted into the second list. */
temp = CreateNode ();
/* Store the contents of the original question and
correct answer that the user was just being asked
into the data portion of the temporary node that
was just created. */
SetData (temp, insertedQuestion);
/* Insert the temporary node into the second list. */
Insert (headListPtr2, temp);
/* Free the memory that was used to create the temporary
node. */
free (temp);
/* Set the node pointer referencing the current node
(the current question in the quiz) to point to the
next node in the list, or the next question in the
quiz. */
curr = curr -> next;
/* Delete the question and its correct answer,
which was just asked to the user, from the first
list. */
Delete (headListPtr1, insertedQuestion.question);
}
else
{
/* Set the node pointer referencing the current node
(the current question in the quiz) to point to the
next node in the list, or the next question in the
quiz. */
curr = curr -> next;
}
}
/* Calculate the user's percentage of questions that were
answered correctly during the first trial of the quiz. */
scoreTrial1 = CalculateScore ((float)correctAnswerCounter,
(float)numberOfTotalQuestions);
/* Display the user's score and tell him/her to retry the
questions that were answered incorrectly. */
printf ("Your score is %.2f%%\n", scoreTrial1);
printf ("Improve your score by repeating the ones you missed.\n\n\n");
/* Return the number of questions that were answered
correctly by the user during this trial so that the
score can be recalculated in the second trial. */
return correctAnswerCounter;
}
Thanks in advance,
Mistro116
