Linked list problem

I want to reverse every three values of my linked list but it it gives me a SIGSEGV error.Can someone tell me what is wrong with the code? Thanks in advance. (eg. for input : 1->2->3->4->5->6->7->8 , output should be 3->2->1->6->5->4->7>8 ) Here is the link to my code: http://ideone.com/C1C1qy