adding values in linked list to a variable

Question

I am creating C program to add up the values in the nodes in Linked List by traversing using while loop.

I have coded the following:

#include <stdio.h>

int main (void)
 {
   struct entry
      {
      int            value;
      struct entry   *next;
      };

   struct entry   n1, n2, n3;
   struct entry   *list_pointer = &n1;
   int sum;
   n1.value = 100;
   n1.next  = &n2;

   n2.value = 200;
   n2.next  = &n3;

   n3.value = 300;
   n3.next  = (struct entry *) 0;    // Mark list end with null pointer

   while ( list_pointer != (struct entry *) 0 ) {
        sum += list_pointer->value;
        list_pointer = list_pointer->next;
     }

  printf ("%i\n", sum);


 return 0;
}

However I am getting the following output:

Instead of getting 600 as the output

You have never initialized sum, so its value is undefined. It contains whatever rubbish was on the stack where it's now stored. You should do `int sum = 0`. Also, please don't use nested struct declarations unless you have a really good reason to do so (in this case, you should pull `entry` out of `main`). — user4520, Nov 15 '15 at 15:13

score 4 · Accepted Answer · edited May 23 '17 at 12:30

  int sum;

Here you're creating a stack variable; the C standard doesn't say anything about its value, and in practice it will contain whatever random bytes were at the memory location where it's now stored. For more information on this, see here: What happens to a declared, uninitialized variable in C? Does it have a value?

You should explicitly initialize it to zero:

  int sum = 0;

On another note, there's absolutely no reason for entry to be defined inside main (in general you should avoid nested struct declarations unless you have a good reason not to).

adding values in linked list to a variable

1 Answers1