Queue List with infinit loop

[alphasil]

Hi....again

I'm having a little problem with an infinite loop, all works normally except the print function who never stop

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


typedef struct eng
{
    char nomes[100];
    char curso[100];
    char inst[100];
    int nota;
    char curri[100];
}INFO;


typedef struct elemento
{
    INFO nodo;
    struct elemento *seguinte;
    struct elemento *anterior;
}ELEM;


int enqueue(INFO info, ELEM **initLista, ELEM **fimLista)
{
    ELEM *novo;
    novo=(ELEM*)malloc(sizeof(ELEM));
    if(novo==NULL)
    {
        printf("Erro na lista");
        return -1;
    }
    novo->nodo=info;
    novo->seguinte=NULL;
    novo->anterior=NULL;
    if(*initLista==NULL)
    {
        *initLista=novo;
        *fimLista=novo;
    }
    novo->anterior=novo;
    (*fimLista)->seguinte=*fimLista;
    *fimLista=novo;
    return 0;
}


int print(ELEM *initLista)
{
    ELEM *aux;
    if(initLista==NULL){
                       printf("lista vazia!\n");
                       return -1;
                       }
    aux=initLista;
    for(aux=initLista;aux!=NULL;aux=aux->seguinte)
    {
        printf("%s %s %s %d %s\n",aux->nodo.nomes,aux->nodo.curso,aux->nodo.inst,aux->nodo.nota, aux->nodo.curri);
        aux=aux->seguinte;
    }
    return 0;
}


int listarMaiorCatorze(ELEM *initLista)
{
    ELEM *aux;
    aux= initLista;
    if(aux->nodo.nota>14)
    {
        printf("%s  %d", aux->nodo.nomes,aux->nodo.nota);
        aux=aux->seguinte;
    }
    return 0;
}
int nextOnList(ELEM *initLista)
{
    //printf(initLista->seguinte);
    
    return 0;
}
int main()
{
    ELEM *initLista=NULL, *fimLista=NULL;
    INFO info;
    int op;
    char buf[30];
    do
    {
        printf("Name: \n");
        fgets(info.nomes, 100, stdin);
        printf("Degree: \n");
        fgets(info.curso, 100, stdin);
        printf("Institution: \n");
        fgets(info.inst, 100, stdin);
        printf("Grade: \n");
        fgets(buf, 100, stdin);
        sscanf(buf, "%d", &info.nota);
        printf("Curriculum: \n");
        fgets(info.curri, 100, stdin);
        printf("More records? (0-to leave) \n");
        scanf("%d", &op);
        getchar();
    }
    while(op!=0);
    enqueue(info,&initLista, &fimLista);
    print(initLista);
    printf("\nCandidatos com mais de 14: \n");
    listarMaiorCatorze(initLista);
    return 0;
}

The print function works with inifinite loop.

If i want to retrieve the next candidate, what do i have to do??

Regards

[Salem]

novo->anterior=novo;
(*fimLista)->seguinte=*fimLista;
*fimLista=novo;

These should be in an else block, and changed to

else {
  // not an empty list
  novo->anterior=*fimLista;  // points back to the current tail
  (*fimLista)->seguinte=nova; // (old) tail points to the new node
  *fimLista=novo;  // tail updated to point to new end node
}

[whiteflags]

The reason that your print function doesn't work is because your list is broken. I think...

All of the nodes are supposed to be connected. If you want to add to the tail end of a list you have to get the last node then connect the next pointer and prev pointer.

ELEM* tail;
for (tail = initLista; tail->seguinte != NULL; tail = tail->next) 
    /* do nothing */;
tail->seguinte = novo;
novo->anterior = tail;
novo->seguinte = NULL;

This should work for inserting all list nodes at the end. The only special case is a new list where there are no nodes.

I really hope I got everything right since I don't speak your language. Let me know if there is any more I can do and please try to explain what you can.

[alphasil]

Hi Salem
Thanks

Now i have a segmentation fault in:

int print(ELEM *initLista)
{
    ELEM *aux;
    if(initLista==NULL){
                       printf("lista vazia!\n");
                       return -1;
                       }
    aux=initLista;
    for(aux=initLista;aux!=NULL;aux=aux->seguinte)
    {
        printf("%s %s %s %d %s\n",aux->nodo.nomes,aux->nodo.curso,aux->nodo.inst,aux->nodo.nota, aux->nodo.curri);
        aux=aux->seguinte;
    }
    return 0;
}

for(aux=initLista;aux!=NULL;aux=aux->seguinte)

[Salem]

Isn't this where you start using a debugger?

I mean, what are you going to do when the programs get 100 times larger, and it starts segfaulting?
Learn how to use the debugger now, and you'll be well prepared for the larger programs to come.

[christop]

    for(aux=initLista;aux!=NULL;aux=aux->seguinte)
    {
        printf("%s %s %s %d %s\n",aux->nodo.nomes,aux->nodo.curso,aux->nodo.inst,aux->nodo.nota, aux->nodo.curri);
        aux=aux->seguinte;
    }

You wrote aux=aux->seguinte at the end of the loop body and in the for statement itself. If the first statement (in the loop body) hits the NULL node, the second statement (in the for statement) will dereference a NULL pointer.

[alphasil]

Hi Christop

Thank you, fixed now.

If i want to print the front of the list, how should i do??