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POReversing the elements of a double linked list in C
 

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    <p>This is my approach-Keep a pointer at the start of the list and a pointer at the end of the list.Advance the head pointer forward and the tail pointer backward until they point the same. Interchange the values before forwarding.The function throws a segmentation fault when it is called.Why is it so? This is my structure for the nodes of the list</p> <pre><code>struct dll { int number; struct dll *next; struct dll *prev; }; </code></pre> <p>This is my function for reversing the list and the main</p> <pre><code> int count=0; void reverse(struct dll **root) { int temp; struct dll *tail=NULL; struct dll *temproot=NULL; temproot =(*root); for(;(temproot)-&gt;next !=NULL;(temproot)=(temproot)-&gt;next); //traversing to the end tail= temproot; while(((*root)-&gt;next != tail-&gt;prev) || ((*root)-&gt;next != tail))//one for even no. of nodes and one for odd no.of nodes { temp=(*root)-&gt;number; //swapping the numbers (*root)-&gt;number=tail-&gt;number; tail-&gt;number=temp; (*root)=(*root)-&gt;next; tail=tail-&gt;prev; } //even after they are same, values need to be changed one last time temp=(*root)-&gt;number; (*root)-&gt;number=tail-&gt;number; tail-&gt;number=temp; (*root)=(*root)-&gt;next; tail=tail-&gt;prev; } void insert(struct dll **root,int num) { struct dll *temp; if(count==0) { if((*root)==NULL) { (*root)=(struct dll *)malloc(sizeof(struct dll)); (*root)-&gt;next=NULL; (*root)-&gt;prev=NULL; (*root)-&gt;number=num; count++; printf("\n%d",count); } } else if((*root)-&gt;next==NULL) { temp=(struct dll *)malloc(sizeof(struct dll)); temp-&gt;next=NULL; temp-&gt;prev=(*root); temp-&gt;number=num; (*root)-&gt;next=temp; count++; printf("\n%d",count); } else { insert(&amp;(*root)-&gt;next,num); } } main() { struct dll *head=NULL; int i,n,num; while(1) { printf("Enter 1 for insert, 3 for reverse, 0 for exit\n"); scanf("%d",&amp;n); switch(n) { case 1:printf("Enter number\n"); scanf("%d",&amp;num); insert(&amp;head,num); break; case 3:reverse(&amp;head);break; case 0:exit(0); default:printf("Enter correct value\n"); } } } </code></pre>
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    1. COWhat line is the segfault on?
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    2. COI am a beginner, how do u check what line the segfault is on?
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    3. COThe best way is to run it in a debugger. I suppose if you don't want to learn how to use a debugger right now you could even just put a `printf` after every line and see which is the last printed.
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