error in c program for binary addition using doubly linkedlist

when i keep a watch, even though initially head1 is NULL it doesn't execute following lines

if(head1==NULL)
{
head1=move;
}


the code is here, please help me

Code:

---

  #include<stdio.h>
#include<conio.h>
#include<alloc.h>

typedef struct linkedlist
{
        int d;
        struct linkedlist *next;
        struct linkedlist *prev;
}node;

node * createnode(int data)
{
        node *newnode;
        newnode = (node *)malloc(sizeof(node));
        newnode->d=data;
        newnode->next=newnode->prev=NULL;
        return newnode;
}


void main()
{
        int n1,n2,temp,i,sum,carry;
        node *head1,*head2,*head3,*move,*move1,*move2,*move3;

        clrscr();
        head1=head2=head3=NULL;

        printf("\n\nEnter no of bits of first no: ");
        scanf("%d",&n1);
        printf("\n\nEnter Binary no: ");

        for(i=0;i<n1;i++)
        {
                scanf("%d",&temp);

                move=createnode(temp);

                if(head1==NULL)
                {
                        head1=move;
                }

                else
                {
                        move->next=head1;
                        head1->prev=move;
                        head1=move;
                }

        }


        printf("\n\nEnter no of bits of second no: ");
        scanf("%d",&n2);
        printf("\n\nEnter Binary no: ");

        for(i=0;i<n2;i++)
        {
                scanf("%d",&temp);

                move=createnode(temp);

                if(head2==NULL)
                {
                        head2=move;
                }

                else
                {
                        move->next=head2;
                        head2->prev=move;
                        head2=move;
                }

        }

        /* *********** create linkedlist for addition ********** */

        move1=head1;
        move2=head2;
        move3=head3;

        while(head1!=NULL || head2 !=NULL)
        {
                if(head3==NULL)
                {
                        head3=createnode(0);
                }
                else
                {
                move=head3;

                while(move->next!=NULL)
                        move=move->next;

                move->next=createnode(0);
                }

                move1=move1->next;
                move2=move2->next;

        }

        /* *********** binary addition ********** */

        move1=head1;
        move2=head2;
        move3=head3;

        carry=0;

        while(move3!=NULL)
        {

                sum=(move1->d)+(move2->d)+carry;


                if(sum==3)
                {
                        move3->d=1;
                        carry=1;
                }
                else if(sum==2)
                {
                        move3->d=0;
                        carry=1;
                }
                else if(sum==1)
                {
                        move3->d=1;
                        carry=0;
                }
                else
                {
                        move3->d=0;
                        carry=0;
                }

                move1=move1->next;
                move2=move2->next;
                move3=move3->next;

        }
/* *********** Display binary addition ********** */

        move=head3;
        printf("\n\nAddition is :\n\n");
        while(move!=NULL)
        {
                printf("  %d",move->d);
        }

        getch();
}

---

Quote:

---

Originally Posted by gaurav9991

when i keep a watch, even though initially head1 is NULL it doesn't execute following lines

Code:

---

if(head1==NULL)
                {
                        head1=move;
                }

---

---

Sure it does! Why would you think that it does not?

By the way, void main is wrong. It must be int main.

I'm sorry sir, but it doesn't !
I'm using Turbo c++ editor version 3.0 , is it a problem due to editor ?
i have faced the same problem with two different machines but the same editor

thanks for reply

That wasn't meant to be a rhetorical question. I was wondering why you thought it wasn't running that code, because I could imagine the scenario where in a release build the compiler effectively does this:

Code:

---

                if(head1==NULL)
                {
                        goto label: //head1=move;
                }

                else
                {
                        move->next=head1;
                        head1->prev=move;
                label:
                        head1=move;
                }

---

So it would appear to jump over the if block when stepped through.

However that was a long shot. The most likely scenario is that you're using a horribly broken and outdated compiler such as Turbo C++.
Visual Studio 2008 Express and Code Blocks are two good free alternatives, where the above code would work as expected.

I've never had much luck with debuggers. When the compiler optimizes code placement for loops, the breakpoints get odd behavior. I think the above code works perfectly... it's just the stepping debugger is confused.