Question

I need help with the following code about linked lists:

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

struct nodo {
    int d;
    struct nodo *next;
};

struct nodo *full();

int main()
{
    struct nodo *l;
    /* l=(struct nodo *)malloc(sizeof(struct nodo)); */
    l = full();
    while(l!=NULL) {
        printf("-->%d\n", l->d);
        l  =l->next;
    }
    system("PAUSE");
}
struct nodo *full()
{
    int i;
    struct nodo *head, *nes;
    head = (struct nodo *)malloc(sizeof(struct nodo));
    head->next = NULL;
    for(i = 1; i < 5; i++) {
        nes = (struct nodo *)malloc(sizeof(struct nodo));
        printf("Insert the %d element:\n", i);
        scanf("%d", &nes->d);
        nes->next = head;
        head = nes;
    }
    return head;
}

If I try for example to input 1, 2, 3, 4, I get the following output:

 -->4
 -->3
 -->2
 -->1
 -->9708864

Why do I get the last number? What’s wrong with my code?

Answer 1

As @Vinska pointed out in the comments, line 3 of full() is not necessary; it is creating an extra node.

The line in question is

head = (struct nodo *)malloc(sizeof(struct nodo));

Instead, say

head = NULL

With your existing code, your linked list has 5 elements. The first one is created on the aforementioned line. The remaining four items are created in the loop, as expected, for a total of 5 elements.

The 9708864 number is a garbage value. It is whatever happened to be in memory when you called malloc(). This is why you have to initialize all of your variables! Or, in this case, use memset() or calloc() to set those blocks to some sane value. (However, that line is completely superfluous here anyway.)

Good luck!