Doubly Linked List insert function - data-structures

Question

I am having problem with this code.Can someone help me to fix it ?
Problem is in insert function especially with malloc(allocating).I don't understand why I cannot malloc.It is not printing the debug text.
#include<stdlib.h>
#include<stdio.h>
#define TRUE 1
#define FALSE 0
struct Node{
int data;
struct Node* next;
struct Node* prev;
};
struct ListRecord
{
struct Node *head;
struct Node *tail;
int length;
};
typedef struct ListRecord *DoubleList;
DoubleList createList()
{
return NULL;
}
DoubleList MakeEmptyList(DoubleList l)
{
l = (struct ListRecord*)malloc(sizeof(struct ListRecord));
if(l==NULL)
{
printf("Memory allocation failed!");
}
else
{
l->head->next=NULL;
l->head->prev=NULL;
l->tail=l->head;
l->length=0;
}
}
DoubleList InsertListAtPosition(DoubleList l,int pos,int val)
{
struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
printf("debug");
if(newNode==NULL)
{
printf("debug");
newNode->data=val;
newNode->next=NULL;
newNode->prev=NULL;
if(pos > l->length+1)
{
pos=l->length+1;
}
else if(pos==l->length+1)
{
struct Node *iterator=l->head;
while(iterator->next != NULL)
{
iterator=iterator->next;
}
iterator->next=newNode;
newNode->prev=iterator;
newNode->next=NULL;
}
else
{
struct Node* iterator=l->head;
int i;
for(i=0;i<pos;i++)
iterator=iterator->next;
newNode->next=iterator->next;
newNode->prev=iterator;
iterator->next->prev=newNode;
iterator->next=newNode;
}
l->length++;
}
else
{
printf("Memory allocation failed!");
}
}
int DeleteListAtPosition(DoubleList l,int pos)
{
int value;
if(l==NULL)
{
printf("List is empty");
return 0;
}
else
{
if(pos==1)
{
struct Node* iterator=l->head;
value=iterator->data;
free(iterator);
return value;
}
else
{
struct Node* iterator=l->head;
int i;
for(i=1;i<pos;i++)
iterator=iterator->next;
if(iterator->next==NULL)
{
value=iterator->data;
free(iterator);
return value;
}
else
{
iterator->prev->next=iterator->next;
iterator->next->prev=iterator->prev;
free(iterator);
}
}
}
}
void printList(DoubleList l) {
struct Node* temp = l->head;
printf("Forward: ");
while(temp != NULL) {
printf("%d ",temp->data);
temp = temp->next;
}
printf("\n");
}
int main(){
DoubleList myList;
int exit,pos,value;
char command;
myList=createList();
exit=FALSE;
while(!exit)
{
fflush(stdin);
printf("\nMenu:\n m)akeEmpty\n i)nsert\n e)xit\n");
scanf("%c", &command);
fflush(stdin);
switch(command)
{
case 'm':
myList = MakeEmptyList(myList);
break;
case 'i':
printf("Enter position to be added: ");
scanf("%d",&pos);
printf("Enter value to be added: ");
scanf("%d",&value);
InsertListAtPosition(myList,pos,value);
//printList(myList);
break;
case 'e':
exit = TRUE;
break;
default:
printf("command not recognized\n");
break;
}
}
printf("\n\n");
system("PAUSE");
return 0;
}

Answer 1

Here is the working code,
#include<stdlib.h>
#include<stdio.h>
#include <bits/stdc++.h>
#define TRUE 1
#define FALSE 0
using namespace std;
struct Node{
int data;
struct Node* next;
struct Node* prev;
};
struct ListRecord
{
struct Node *head;
struct Node *tail;
int length;
};
typedef struct ListRecord *DoubleList;
DoubleList createList()
{
return NULL;
}
DoubleList MakeEmptyList()
{
DoubleList l;
l = (struct ListRecord*)malloc(sizeof(struct ListRecord));
if(l==NULL)
{
printf("Memory allocation failed!");
}
else
{
struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
newNode->next = NULL;
newNode->prev = NULL;
l->head = newNode;
l->tail=l->head;
l->length=0;
}
return l;
}
DoubleList InsertListAtPosition(DoubleList l,int pos,int val)
{
struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
if(newNode != NULL)
{
newNode->data=val;
newNode->next=NULL;
newNode->prev=NULL;
if(pos > l->length)
{
pos=l->length+1;
}
else if(pos==l->length)
{
struct Node *iterator=l->head;
while(iterator->next != NULL)
{
iterator=iterator->next;
}
iterator->next=newNode;
newNode->prev=iterator;
newNode->next=NULL;
}
else
{
struct Node* iterator=l->head;
int i;
for(i=0;i<pos;i++)
iterator=iterator->next;
newNode->next=iterator->next;
newNode->prev=iterator;
iterator->next->prev=newNode;
iterator->next=newNode;
}
l->length++;
}
else
{
printf("Memory allocation failed!");
}
}
int DeleteListAtPosition(DoubleList l,int pos)
{
int value;
if(l==NULL)
{
printf("List is empty");
return 0;
}
else
{
if(pos==1)
{
struct Node* iterator=l->head;
value=iterator->data;
free(iterator);
return value;
}
else
{
struct Node* iterator=l->head;
int i;
for(i=1;i<pos;i++)
iterator=iterator->next;
if(iterator->next==NULL)
{
value=iterator->data;
free(iterator);
return value;
}
else
{
iterator->prev->next=iterator->next;
iterator->next->prev=iterator->prev;
free(iterator);
}
}
}
}
void printList(DoubleList l) {
struct Node* temp = l->head;
printf("Forward: ");
while(temp != NULL) {
printf("%d ",temp->data);
temp = temp->next;
}
printf("\n");
}
int main(){
DoubleList myList;
int exit,pos,value;
char command;
exit=FALSE;
while(!exit)
{
fflush(stdin);
printf("\nMenu:\n m)akeEmpty\n i)nsert\n e)xit\n");
scanf("%c", &command);
fflush(stdin);
switch(command)
{
case 'm':
myList = MakeEmptyList();
break;
case 'i':
printf("Enter position to be added: ");
scanf("%d",&pos);
printf("Enter value to be added: ");
scanf("%d",&value);
if(myList == NULL) {
myList = MakeEmptyList();
}
InsertListAtPosition(myList,pos,value);
//printList(myList);
break;
case 'e':
exit = TRUE;
break;
default:
printf("command not recognized\n");
break;
}
}
printf("\n\n");
system("PAUSE");
return 0;
}
So you were making the following mistakes,
Your MakeEmptyList method is returning nothing, it should return l.
Inside you insert you were checking with length + 1, instead of only length, so it was causing pointer related errors.