Error in list linked in C

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Error in list linked in C

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#1 by (1 votes)

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I'm making a list linked in C of integer data that is saved in it until you press Enter. The problem is that the last element that saves is garbage, because it keeps a dynamic memory address and still can not find the error.

Here is my code:

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

typedef struct nodo
{
   int dato;
   struct nodo *siguiente;
}lista;

int main(void)
{
int dato;
lista *list = (lista *)malloc(sizeof(struct nodo)), *aux = list;

printf("Ingresa datos enteros (enter para terminar): ");
do
{
    scanf("%d", &dato);
    list->dato = dato;
    list->siguiente = (lista *)malloc(sizeof(struct nodo));
    list = list->siguiente;

}while(getchar() != 10);
list->siguiente = NULL;

while(aux != NULL)
{
    printf("%d   %d\n", aux, aux->dato);
    aux = aux->siguiente;
}

return 0;
 }

And this is an image of the problem I'm referring to

c

asked by EmmanCanVaz_95 14.06.2017 в 04:30

source

1 answer

Problem with ORDER BY: DESC Prevent web portal from skipping the login

score 1 · Accepted Answer

Your problem is in the internal logic that you are using. Let's analyze in detail your do ... while loop:

do
{
  scanf( "%d", &dato );
  list->dato = dato;
  list->siguiente = (lista *)malloc( sizeof( struct nodo ) );
  list = list->siguiente;   
}while( getchar( ) != 10 );
list->siguiente = NULL;

You read the keyboard data.

You save it in the current node.

You create a new empty node (without initializing).

You advance your pointer to that new node that you have created.

If the user presses ENTER , you end the loop.

Look closely. You end the loop leaving the last node uninitialized .

One possible solution would be to use an auxiliary variable, so as not to lose sight of the previous node. As you can see, I have also changed the way to finish the data entry: in my system, your solution with getchar( ) does not work; Now, you have to enter a letter to finish.

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

typedef struct nodo {
  int dato;
  struct nodo *siguiente;
}lista;

int main( void ) {
  int dato;
  lista *list = malloc( sizeof( lista ) );
  lista *aux = list;
  lista *prev = list;

  printf( "Ingresa datos enteros (una letra para terminar):\n");

  while( scanf( "%d", &dato ) ) {
    list->dato = dato;
    prev = list;
    list->siguiente = malloc( sizeof( lista ) );
    list = list->siguiente;
  };

  if( aux == list ) {
    printf( "¡ La lista está vacía !\n" );
    free( aux );
    aux = NULL;
  } else {
    free( prev->siguiente );
    prev->siguiente = NULL;
  }

  while( aux ) {
    printf( "%p: %d\n", aux, aux->dato );
    aux = aux->siguiente;
  }

  return 0;
}

There is an extra part, just after the while( ) , which is responsible for controlling the correction of the list: if it is empty, it indicates it, and if it is not empty, it eliminates the last node and appropriately places the pointer siguiente in the penultimate node.