C programming : Linked Lists

Question

Im trying to implement a program using a bi-dimensional array of linked lists, to store lists of products and their quantity. For now, i've only done functions do add and show what's inside the list of the first array element t[0][0]. There's no error's when I add the product name and quantity, but when I try to show the list, I get no result. Can you check if im making some mistakes? Thanks for the help.

typedef struct object product, *pprod;
struct object{
    char name[100];
    int quantity;
    pprod next;
};

product t[4][3];


int is_empty(pprod p)
{
    if(p == NULL)
        return 1;
    else
        return 0;
}
void show_info(pprod p)
{
    while(p != NULL)
    {
        printf("%s\t%d\n",
               p->name, p->quantity);
        p = p->next;
    } }

void get_data(pprod p)
{
    printf("name: ");
    scanf("%s",p->name);
    printf("quantity: ");
    scanf("%d",&p->quantity);
    p->next = NULL;
}

pprod insert_beginning(pprod p)
{
    pprod new;
    if((new = malloc(sizeof(product))) == NULL)
        printf("Error allocating memory\n");
    else
    {
        get_data(new);
        new->next = p; } p = new;
    return p;
}


int main(int argc, char *argv[]){
    insert_beginning(t[0][0].next);
    show_info(t[0][0].next);
    printf("%d",is_empty(t[0][0].next));


}

Not related, but you may want to reconsider naming variables 'new'. 'new' is a commonly reserved keyword in c++ and it can be a bit confusing to read. — Captain Skyhawk
– Captain Skyhawk, Commented May 24, 2013 at 20:48
Oops. Sorry about that, never did anything in C++. And thanks for the heads up — Carla Pateiro
– Carla Pateiro, Commented May 24, 2013 at 20:55

scottt · Accepted Answer · 2013-05-26 17:48:58Z

1

You at least want something like:

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

typedef struct object product, *pprod;
struct object{
    char name[100];
    int quantity;
    pprod next;
};

product t[4][3];


int is_empty(pprod p)
{
    if(p == NULL)
        return 1;
    else
        return 0;
}
void show_info(pprod p)
{
    while(p != NULL) {
        printf("%s\t%d\n",
                p->name, p->quantity);
        p = p->next;
    }
}

void get_data(pprod p)
{
    printf("name: ");
    scanf("%s",p->name);
    printf("quantity: ");
    scanf("%d",&p->quantity);
    p->next = NULL;
}

pprod insert_beginning(pprod *p)
{
    pprod new;
    if ((new = malloc(sizeof(product))) == NULL) {
        printf("Error allocating memory\n");
        assert(0);
    } else {
        get_data(new);
        new->next = *p;
        *p = new;
    }
    return *p;
}


int main(int argc, char *argv[])
{
    insert_beginning(&t[0][0].next);
    show_info(t[0][0].next);
    printf("%d",is_empty(t[0][0].next));
    return 0;
}

But this obviously still wastes all the storage space for name and quantity in t[0][0]. You can fix that by changing

product t[4][3];

to

pprod t[4][3];

and

int main(int argc, char *argv[])
{
        insert_beginning(&t[0][0].next);
        show_info(t[0][0].next);
        printf("%d",is_empty(t[0][0].next));
        return 0;
}

to

int main(int argc, char *argv[])
{
        insert_beginning(&t[0][0]);
        show_info(t[0][0]);
        printf("%d",is_empty(t[0][0]));
        return 0;
}

I also don't get why you want to organize t as a two dimensional linked list. (EDIT: Carla explained that in the comments)

Error in show_all()

You had two off by 1 errors in show_all()

void show_all()
{
    int i,j;
    for(i=0;i<=3;i++){
        for(j=0;j<=2;j++){
            printf("C:%dA:%d\n",i,j);
            show_info(t[i][j]);
        }
    }
}

You've changed the dimensions of t to be t[3][2] so it should be i = 0; i < 3; i++ and j = 0; j < 2; j++ instead. Here's how C programmers would usually handle this:

#define ARRAY_SIZE(a) (sizeof((a))/sizeof((a)[0]))

void show_all()
{
    int i,j;
    for(i=0;i<ARRAY_SIZE(t);i++){
        for(j=0;j<ARRAY_SIZE(t[0]);j++){
            printf("C:%dA:%d\n",i,j);
            show_info(t[i][j]);
        }
    }
}

edited May 26, 2013 at 17:48

answered May 24, 2013 at 20:50

scottt

7,30829 silver badges39 bronze badges

Sign up to request clarification or add additional context in comments.

9 Comments

Carla Pateiro Over a year ago

The problem proposed its based on a warehouse, composed by 4 corridors, each corridor has 3 shelfs. The products are placed inside the shelfs, by product name and quantity. I thought I could make and 2d array to select [corridor][shelf], and inside a linked list for the products. How can I avoid wasting that storage space?

scottt Over a year ago

@CarlaPateiro, I've made an edit to my answer and have one more suggestion for you.

Carla Pateiro Over a year ago

With the edit, "t[4][3]" its now an 2d-array of pointers right? Thanks the suggestion :)

scottt Over a year ago

right ^_^. If you're using insert_beginning() for everything and it calls malloc() then that's the logical change.

Carla Pateiro Over a year ago

Sorry to bother you again Scott. When I use the insert_beginning() function to add products in another array position, like [0][2], they duplicate in the position [1][0]. Do you know why? Thanks :)

|

Collectives™ on Stack Overflow

C programming : Linked Lists

1 Answer 1

Error in show_all()

9 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Error in show_all()

9 Comments

Your Answer

Sign up or log in

Post as a guest

Related