why does the below program terminate giving segmentation fault ?

[radha gogia]

#include<stdio.h>
#include<malloc.h>
struct node 
{int a;
struct node *next;
};
int main()
{
int i=0;
struct node *p,*head;
for( i=0;i<5;i++)
 { 
p=(struct node*)malloc(sizeof(struct node));
 if(head==NULL)
{
head=p;
head->next=NULL;
}
else
{
p->next=head;
head=p;
}
}
for(i=0;i<2;i++)
{
printf("%d  ",head->a);
head=head->next;
}
return 0;
}

Here only 2 nodes are created with some garbage value , but after the values are printed , why do I get a segmentation fault ?

[hpmachining]

You are not initializing head. It is probably not NULL when the program enters the for loop.

[radha gogia]

So what is the issue then , it will directly be going to else part and continue with p->next=head and head=p , what's the issue here ?

[hpmachining]

If head is some garbage value, I am thinking the p->next=head line will be assigning an invalid address to p->next. I could be wrong, but you could try setting head to NULL before entering the loop to see if it fixes it. I tried your program with Visual Studio and GCC. VS wouldn't compile without initializing and GCC didn't give me the seg fault, so I can't say for sure if that is the problem.