c - 从 C 中的 FIFO 链接列表中弹出函数不起作用

Question

几天后，我将参加一场关于 C 语言的非常重要的考试。我很棒的老师给了我一点帮助，除了其他事情之外，还给了我这次考试。这里我必须让函数“pop”。我几乎整个周末都在尝试，但仍然不起作用，这让我感到沮丧。也许你们可以帮助我。我希望 pop 是 FIFO 的。

#include <stdio.h>

typedef struct test NODE;
typedef NODE *NV;

struct test
{
  int data;
  NV next;
};

int empty(NV);
int geeftop(NV);
void pop(NV, NV *, NV *);
void push(NV *, NV *, int);

int main(void)
{
  int k, number;
  int controle;
  NV start;
  NV staart;
  staart = NULL;
  start = NULL;

  do
  {
    system("CLS");
    printf("\nKeuzemenu:\n");
    printf("[1] = ADD.\n");
    printf("[2] = DELETE.\n");
    printf("[3] = IS IT EMPTY?.\n");
    printf("[4] = Stop.\n\n");
    printf("type your number: ");

      do
      {
        scanf("%d", &k);
      } while (k <= 0 || k >= 5);

      switch (k)
      {
        case 1: printf("give a number: ");
                scanf("%d", &number);
                push(&start, &staart, number);
                break;
        case 2: if (!empty(start))
                {
                  pop(start, &start ,&staart);
                  printf("\ntop is deleted.\n\n");
                }
                else
                  printf("\nerror.\n\n");
                system("PAUSE");
                break;
        case 3: controle = empty(start);
                if (controle == 1)
                  printf("\nits emtpy.\n\n");
                else
                  printf("\nniet empty.\n\n");
                system("PAUSE");
                break;
        default: break;
      }
  } while (k != 4);

  system("PAUSE");
  return 0;
}

int empty(NV phuidige)
{
  return (phuidige == NULL);
}

void pop(NV phuidige2, NV *phuidige, NV *pstaart)
{
  if ((phuidige2) -> next  == NULL)
  {
    NV weg;
    NV weg2;
    weg = *pstaart;
    weg2 = *phuidige;
    pstaart = NULL;
    phuidige2 = NULL;
    free (pstaart);
    free (phuidige2);
  }
  else
  {
    while ((phuidige2) ->  next -> next != (NULL))
    {
      phuidige2 = phuidige2 -> next;
    }
  }

  {
    phuidige2 -> next  = NULL;
    NV weg;
    weg = *pstaart;
    *pstaart = NULL;
    free (weg);
  }
}

void push(NV *phuidige, NV *pstaart, int x)
/* pre er is ruimte op de stack;
   post stack(post) = stack(pre) U {x}; */
{
  NV hulp;

  hulp = malloc(sizeof(NODE));
  hulp -> data = x;
  hulp -> next = *phuidige;
  *phuidige = hulp;

  if (*pstaart == NULL)
  {
    *pstaart = hulp;
  }
  else
  {
  }
}

Answer 1

您确实应该检查 scanf 的返回值，k 的值未初始化。基本上 pop 应该只返回你的头指针，并将头指针前进到下一个元素 - 随时检查 null 。