Thread: i have problem creating a linked list

the problem says to ask input from user about name and age and store it in linked lists also ask him a number each time he finishes putting data in the linked list if he gives 1 that means he wants to store more if he gives 0 that means he doesnt want to store anything else

then we want to show the results on screen

here is what i ve done so far

Code:

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

struct node{
       char name[20];
       int age;
       struct node *next;
       };

struct node *prosthiki(int il, char on[]){
       
       struct node *a;
       a = malloc(sizeof(struct node));
       a->age = il;
       strcpy(a->name,on);
       a->next = NULL;
       
       return a;
       
       }
       
struct node *prosthiki2(int il, char on[], struct node *lol){
       
       lol = malloc(sizeof(struct node));
       lol->age = il;
       strcpy(lol->name,on);
       lol->next = NULL;
       return lol;
       
       
       }

void show(struct node *head){
     struct node *l;
     l=head;
     while(l!=NULL){
                    printf("%d ",l->age);
                    printf("%s\n",l->name);
                    l = l->next;
                    }
     }
     
int main(void){
    int check = 1;
    int count=0;
    struct node *head = NULL;
    struct node *current = NULL;
    char on[20];
    int gad;
    
    while (check!=0){
          
          printf("give name: \n");
          scanf("%s",on);
          fflush(stdin);
          printf("give age: \n");
          scanf("%d",&gad);
          fflush(stdin);
          if (count==0){
                        head = prosthiki(gad,on);
                        }
          else {
               current = prosthiki2(gad,on,current);
               head->next = current;       
               current = current->next;
               
               }
          printf("success!!!!\n\n");
          printf("do you want to continue: \n");
          scanf("%d",&check);
          fflush(stdin);
          count++;
          }
    
    show(head);
    getchar();
    return 0;
}

it works for 2 nodes and 1 node, it doesnt work for more than 2 nodes

what am i doing wrong?

thanks

ps: it's not an assignment i was reading an ebook to understand linked lists and came up with this problem

Originally Posted by nik2

Code:

          else {
               current = prosthiki2(gad,on,current);
               head->next = current;       <<-- WRONG
               current = current->next;
               
               }
 
}

For the first to loops it works, but after, that code assigns to the first successor of the head, the current node. That means you have a list with only two elements and each round you lost the reference to the second element.

Originally Posted by flexo87

For the first to loops it works, but after, that code assigns to the first successor of the head, the current node. That means you have a list with only two elements and each round you lost the reference to the second element.

hm yea you're right

this way won't work I guess, I will try to think of another algorithm

The algorithm it's fine, use another reference which points to the Kth-node. Where K is the the value of the variable count, and use it to add the current node to the end of the list. Otherwise you can modify your *prosthiki2() in a way that it scans all the list till the last element and then add the new node. I would choose the first one,... the second is slower (in terms of computation)!

Dear friend,

You did some mistake in the assign the pointer address. I have attach the correct code here. You need to change the coding in the main function only. No need to change any other coding.
Then You need to change the calling of show function also. Because here I have changed some coding.

Code:

 while (check!=0){

          printf("give name: \n");
          scanf("%s",on);
          fflush(stdin);
          printf("give age: \n");
          scanf("%d",&gad);
          fflush(stdin);
          if (count==0){
                        head = prosthiki(gad,on);
                        root=head;  // To copy the address of the main node to some other node 
                        }
          else {
               current = prosthiki2(gad,on,current);
               head->next = current; // To store the current pointer value to the head of next.
               head=current; // To store the current address to the head
               current=current->next; // To store the current of next to current 
               }
          printf("success!!!!\n\n");
          printf("do you want to continue: \n"); 
          scanf("%d",&check);
          fflush(stdin);
  show(root);
    getchar();
    return 0;

Explanation:
==========
In the initial stage the pointer "current" value is null. In the function "prosthiki2" you allocate the memory and return that pointer address. It is correct.

But inside the main function you wrongly assign the address to the head pointer.