Thread: pointer assignment inside a function ???

Hello,

This program has a function alterlist() which takes a node to a list and a function check() as an argument and removes all nodes that return a non-zero value from the function check()


The program works fine . I couldn't understand one thing in the function alterlist() when I try doing

link y = b;

the program gives me an error on running
if I do that I save some condition checking inside the loop since i wouldn't have to vare about where the new list starts, but it doesn't work ??????

Code:

#include<stdio.h>
#include<stdlib.h>


/*  ******************************************************* */
/*  This program does arithmetic operation on a linked list */
/*  ******************************************************* */

typedef struct node *link;

struct node
{
       int item; 
       link next;
};

link makelist(link x, int num);
void printlist(link x);
int check(link x);
link alterlist(link x, int check(link));

int main()
{
    link x = NULL;
    x = makelist(x, 5);
    x = alterlist(x, check);
    printlist(x);
    return 0;
}

link makelist(link x, int num)
{
     int i;
     if(0 == num)
     {
         x = NULL;
         return;
     }
     link a = malloc(sizeof *a);
     x = a;
     a->item = 1;
     if(1 == num)
     {
          a->next = NULL;
          return;
     }
     for(i = 2; i <= num; i++)
     {
         a->next = malloc(sizeof *a);
         a = a->next;
         a->item = i;
         if(i == num)
          {
               a->next = NULL;
               break;
          }
     }
     return x;
}

void printlist(link x)
{
    link b = x;
    while(b != NULL)
    {
         printf("%d, ", b->item);
         b = b->next;   
    }
}


int check(link x)
{
    if (NULL == x)
         return 0;
    else
        return (x->item %2);
}

link alterlist(link x, int check())
{
     link a = x, b; 
     link y = NULL;
     while(a != NULL)
     {
         if(0 == check(a))
         {
              if(a == x)
              {
                   b = a;
                   y = b;
                   a = a->next;
              }
              else
              {
                   b = a;
                   if(NULL == y)
                        y = b;
                   a = a->next;  
              }
         }
         else
         {
              if(a == x)
                   a = a->next;
              else
              {
                  b->next = b->next->next;
                  a = a->next;
              }
         }
     }
     return y;
}

in the function alterlist, you haven't initialised b. it is not a global variable either. so what is it??

that is because the b pointer has not been initialized to NULL,

Code:

link a = x, b=NULL; 
 link y = b;

hope this hepls

s.s.harish

that is because the b pointer has not been initialized to NULL,


Code:
link a = x, b=NULL;
link y = b;

make those changes and remove/comment lines 91, 97 and 98 since b has already been initilaized.

The program still doesn't work ?????

it works fine for me

this is the outout i get

Code:

2, 4,

which compiler are using and what error do you get

i think is that the seg fault

s.s.harish

I am using dev-c++ compiler by bloodshed which one did u try it with ?

no error it just doesn't give me an output when i run the exe file through cmd prompt