如何使用 C 中的链接实现将元素插入和显示到出队

Question

我使用链接实现在 c 中尝试了一个基本的出队程序。 但是它显示了用于将元素插入出队的函数的一些错误。 我也想在出列中显示元素。 下面是我试过的代码。 运行代码时 CLI 不显示任何输出。 由于插入函数中的错误，我不确定删除函数是否也正确。

#include<stdio.h>
#include<stdlib.h>
typedef int DeQueueElement;
typedef enum{FALSE,TRUE} Boolean;
typedef struct node{
    DeQueueElement entry;
    struct node *next, *prev;
}Node;
typedef struct dequeue{
    int count;
    Boolean full;
    Node *front;
    Node *rear;
}DeQueue;
void CreateDeQueue(DeQueue *dq){
    dq->count = 0;
    dq->full = FALSE;
    dq->front = dq->rear = -1;
}
Boolean IsEmpty(DeQueue *dq){
    return (dq->front == NULL && dq->rear == NULL);
}
Boolean IsFull(DeQueue *dq){
    return(dq->full);
}
void InsertRear(DeQueueElement x, DeQueue *dq){
    Node *np;
    np = (Node* )malloc(sizeof(Node));
    if(np == NULL){
        printf("Not enough space\n");
    }
    else{
        if(dq->rear == NULL)
            dq->front = dq->rear = np;
        else{
            np->prev = dq->rear;
            dq->rear->next = np;
            dq->rear = NULL;
            np->next = np;
            np->entry = x;
        }
    }
}
void InsertFront(DeQueueElement x, DeQueue *dq){
    Node *np;
    np = (Node* )malloc(sizeof(Node));
    if(np == NULL)
        printf("Not enough space\n");
    else{
        if(dq->front == NULL)
            dq->rear = dq->front = np;
        else{
            np->next = dq->front;
            dq->front->prev = np;
            dq->front = np;
            np->prev = NULL;
            np->entry = x;
        }
    }
}
void DeleteFront(DeQueue *dq){
    if(dq->front == NULL)
        printf("Underflow\n");
    else{
        Node *temp;
        temp = dq->front;
        dq->front = dq->front->next;
        if(dq->front == NULL)
            dq->rear = NULL;
        else
            dq->front->prev = NULL;
        free(temp);
    }
}
void DeleteRear(DeQueue *dq){
    if(dq->front == NULL)
        printf("Underflow\n");
    else{
        Node *temp;
        temp = dq->rear;
        dq->rear = dq->rear->prev;
        if(dq->rear == NULL)
            dq->front == NULL;
        else
            dq->rear->next = NULL;
        free(temp);
    }
}
 void display(DeQueue *dq) {
        Node *temp;

        if (dq->front->next == dq->rear) {
                printf("Queue is empty\n");
                return;
        }

        temp = dq->front->next;
        while (temp != dq->rear) {
                printf("%d", temp->entry);
                temp = temp->next;
        }
        printf("\n");
  }

int main(){
    DeQueue dq;
    CreateDeQueue(&dq);
    InsertFront(21,&dq);
    InsertFront(1,&dq);
    InsertFront(221,&dq);
    InsertRear(23,&dq);
    InsertRear(36,&dq);
    display(&dq);
}

Answer 1

代码有一些错误，我尝试更正它们并评论我所做的更改。 问题出在CreateDeQueue 、 InsertFront 、 InsertRear和display函数中。

void CreateDeQueue(DeQueue *dq){
    dq->count = 0;
    dq->full = FALSE;
    // dq->front = dq->rear = -1;
    // Change 0: It should be NULL or 0 not -1
    dq->front = NULL;
    dq->rear = NULL;
}
void InsertRear(DeQueueElement x, DeQueue *dq){
    Node *np;
    np = (Node* )malloc(sizeof(Node));
    if(np == NULL){
        printf("Malloc failed\n");
    }
    else{
        np->entry = x;
        np->next = NULL;
        np->prev = NULL;
        if(dq->rear == NULL)
            dq->front = dq->rear = np;
        else{
            np->prev = dq->rear;
            dq->rear->next = np;
            //dq->rear = NULL;
            //Change 1: Why dq->rear to NULL it should point to valid mem location
            dq->rear = np;
        }
        dq->count++;
    }
}
void InsertFront(DeQueueElement x, DeQueue *dq){
    Node *np;
    np = (Node* )malloc(sizeof(Node));

    if(np == NULL)
        printf("Malloc failed. \n");
    else{
        //Change 3: Initialize the newly created struct Node, np
        np->entry = x;
        np->next = NULL;
        np->prev = NULL;

        if(dq->front == NULL)
            dq->rear = dq->front = np;
        else{
            np->next = dq->front;
            dq->front->prev = np;
            dq->front = np;
        }
        dq->count++;
    }
}
void display(DeQueue *dq) {
       Node *temp;
       if (dq->front->next == dq->rear) {
               printf("Queue is empty\n");
               return;
       }
       temp = dq->front;
       // Change 4: Checking temp against dq->rear is not logical i guess
       // temp should  not be NULL. Printing from the front
       while (temp!=dq->rear->next) {
           printf("%d ", temp->entry);
           printf("\n");
           temp = temp->next;
       }
}