linked list again

[St0rM-MaN]

hi all

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

#define ADD "add"
#define PRINT "print"
#define STOP  "STOP"

struct str
{
        char name[50];
        char age[50];
        struct str *next;
};

struct str  *get();

int main()
{
        struct str *current,*root;
        char *command;

        if(!(current=malloc(sizeof(struct str))))
        {
                fprintf(stderr,"Allocating FALID\n");
                exit(1);
        }
        current->next=current;
        root=current;

        printf("Enter Command (add,print):");
        scanf("&#37;s",command);/*fgets is not working why*/
        getchar();

     while(current !=0)
     {
        if(strcmp(command,ADD)==0)
        {
                current = get();
                printf("Your Command:");
                scanf("%s",command);
                getchar();
        }
        else if(strcmp(command,PRINT)==0)
        {
                        current->next=0;/*End The List*/
                        current=root;
                        printf("Name %s",current->name);
                        printf("Age %s\n",current->age);
        }
        else
        {
                fprintf(stderr,"Undefined Command %s\n",command);
                printf("Your Command:");
                scanf("%s",command);
                getchar();/*fllushing input stream*/
        }
     current=current->next;
     }
     printf("By\n");
     return 0;
}

struct str  *get()
{
        struct str *input;
        input=malloc(sizeof(struct str));
        input->next=input;
        printf("Name:\n");
        scanf("%s",input->name);
        printf("Age:\n");
        scanf("%s",input->age);
        return (input);
}

input is ok ;
but
when it comes to the print command
i am stuck in there
here's what i got

storm@St0rM-MaN:~/Desktop/c# ./linked-o
Enter Command (add,print):add
Name:
Fiky
Age:
15
Your Command:add
Name:
Storm
Age:
17
Your Command:add
Name:
Nothing
Age:
400000
Your Commandrint
Name Age
Name Age
By

it's not printing any thing at all
although i make the current->next=0
witch ends the input
and then i make current pointer points to the root pointer witch is the first pointer in the linked list
and when i used fgets to get command it always give me
undefined command
so my questions are
why fgets is not working
and
why it's not printing?

thanks all

[dwks]

Your fgets() was probably not working because you didn't remove the newline from the buffer it filled. Or maybe it's because of this:

char *command;

You cannot read a string into a dangling pointer like that. You have to dynamically allocate memory for command, or declare it as an array.

Also, perhaps you want to read command inside the while loop?

[St0rM-MaN]

right
so what about printing the linked list ?
thanks

[iMalc]

Not part of your problem, but you might want to use stricmp instead of strcmp.

[dwks]

It's actually the way you're creating the list.

        if(strcmp(command,ADD)==0)
        {
                current = get();

You can't just assign current to get(). That won't change root->next or whatever.

The trouble is that you already have an element in the list, then you go to add a new, dynamically allocated element. What to do?

The easiest solution is probably to set root to NULL at first, in case no elements are added to the list. It would complicate the logic somewhat -- when you go to add an element to the list, you have to check if root is NULL -- but you wouldn't waste any memory.

Also, setting input->next to NULL in get() makes more sense than setting it to input and then setting it to NULL in the if(print) conditional. And, at the beginning, current->next would be set to NULL, following this same logic.

[edit]

Not part of your problem, but you might want to use stricmp instead of strcmp.

Then again, you might not. strcmp() is ANSI standard, whereas stricmp() is a POSIX function (and a Borland extension). It's not as portable. If you want a case-insensitive string comparision function, it's best to write your own with tolower() -- unless you want only POSIX compatibility. [/edit]

[St0rM-MaN]

dwks
i will try what you said
thanks

[St0rM-MaN]

You can't just assign current to get(). That won't change root->next or whatever.

The trouble is that you already have an element in the list, then you go to add a new, dynamically allocated element. What to do?

The easiest solution is probably to set root to NULL at first, in case no elements are added to the list. It would complicate the logic somewhat -- when you go to add an element to the list, you have to check if root is NULL -- but you wouldn't waste any memory.

Also, setting input->next to NULL in get() makes more sense than setting it to input and then setting it to NULL in the if(print) conditional. And, at the beginning, current->next would be set to NULL, following this same logic.

The easiest solution is probably to set root to NULL at first

but when i do this i will loss the linked list

Also, setting input->next to NULL in get() makes more sense than setting it to input and then setting it to NULL

i can't get that
if i set input->next to null
each time i call malloc to allocate space for input that will give me a new link right
then i end this link by set ->next to null
am i right ?

[dwks]

What I mean is this.

ITEM *root = NULL;
ITEM *current = root;

if(add_element) {
    if(!root) {
        root = allocate_element();
        root = read_element();
        current = root;
    }
    else {
        current->next = allocate_element();
        current->next = read_element();
        current = current->next;
    }
}

That is, current always points to the previous element in the list, so that you can use current->next to allocate the next element; except when root is NULL, which means that the list is empty.

Alternatively, you could do this.

ITEM *root = NULL;
ITEM **current = &root;

if(add_element) {
    *current = allocate_element();
    *current = read_element();
    *current = &((*current)->next);
}

[St0rM-MaN]

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

struct info
{
        char name[50];
        char age[50];

        struct info *next;
};

struct info * allocate(void);
void get_elements(struct info *t);

#define ADD    "add"
#define PRINT  "print"

int main()
{
                struct info *root;
                struct info *current;
                char *command;
                int x=0;

                root=NULL;

                while(1)
                {
                        printf("Enter Command:");
                        scanf("&#37;s",command);
                        getchar();
                        if(strcmp(command,ADD)==0)
                        {
                                if(root==NULL)
                                {
                                        root=allocate();
                                        get_elements(root);
                                        current=root;
                                }
                                else
                                {

                                        current->next=allocate();
                                        get_elements(current->next);
                                        current=current->next;
                                }
                        }
                        else if(strcmp(command,PRINT)==0)
                        {
                                if(root==NULL)
                                {
                                        fprintf(stderr,"There Is No List\n");
                                        exit(1);
                                }
                                else
                                        {
                                                current=root;
                                                printf("---------------------------------------\n");
                                                printf("Recorde\t\tName\t\tAge\n");
                                                printf("--------------------------------------\n");
                                                while(current!=NULL)
                                                {
                                                        x++;
                                                        printf("%d\t\t%s\t\t%s\n",x,current->name,current->age);
                                                        current=current->next;

                                                }
                                                break;
                                }
                }
                        else
                        {
                        printf("Undefined Command %s\n",command);
                        }
        }
        exit(EXIT_SUCCESS);
}
struct info *allocate()
{
        struct info *t;
                t=malloc(sizeof(struct info));
                return t;
}

void get_elements(struct info *t)
{
        printf("Enter Your Name:");
        scanf("%s",t->name);
        getchar();
        printf("Enter Your Age:");
        scanf("%s",t->age);
        getchar();

}

offffffffffffffffff finally it works
thanks all

[iMalc]

Then again, you might not. strcmp() is ANSI standard, whereas stricmp() is a POSIX function (and a Borland extension). It's not as portable. If you want a case-insensitive string comparision function, it's best to write your own with tolower() -- unless you want only POSIX compatibility.

Perhaps, but for someone who is obviously just beginning to learn to program, I suspect portability is the least of his worries.

[ssharish2005]

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

#define ADD    "add"
#define PRINT  "print"

struct info
{
    char name[50];
    char age[50];
    struct info *next;
};

struct info * allocate(void);
void get_elements(struct info *t);

int main()
{
    struct info *root;
    struct info *current;
    char *command;
    int x=0;

    root=NULL;

    while(1)
    {
        printf("Enter Command:");
        scanf("&#37;s",command);   // You should use fgets, u can avoid using getchar after scanf
        getchar();
        
        if( strcmp(command,ADD)==0 )
        {
            if(root==NULL)
            {
                 root=allocate();
                 get_elements(root);
                 current=root;
            }
            else
            {
                 current->next=allocate();
                 get_elements(current->next);
                 current=current->next;
            }
        }
        else if(strcmp(command,PRINT)==0)
        {
            if(root==NULL)
            {
                 fprintf(stderr,"There Is No List\n");
                 exit(1);
            }
            else
            {
                 current=root;
                 printf("---------------------------------------\n");
                 printf("Recorde\t\tName\t\tAge\n");
                 printf("--------------------------------------\n");
                 while(current!=NULL)
                 {
                      x++;
                      printf("%d\t\t%s\t\t%s\n",x,current->name,current->age);
                      current=current->next;
                 }
                 break;
            }
         }
         else
              printf("Undefined Command %s\n",command);
    }

    getchar();
    return 0;
}

struct info * allocate(void)
{
    return malloc (sizeof struct info);
}

void get_elements(struct info *t)
{
        printf("Enter Your Name:");
        scanf("%s",t->name);   // fgets(t->name,sizeof t->name, stdin);
        getchar();  
        printf("Enter Your Age:");
        scanf("%s",t->age);  // fgets(t->age,sizeof t->age, stdin)
        getchar();
}

You indendation should be good, to be a good programmer. And look at the comments along the code.

ssharish2005

[St0rM-MaN]

Perhaps, but for someone who is obviously just beginning to learn to program, I suspect portability is the least of his worries.

thanks but i am not that level

You indendation should be good, to be a good programmer. And look at the comments along the code.

i am trying
thanks
thanks dwks