c - 双链表。我做的好吗？

Question

我是 C 编程的初学者。我的任务是使用双链表创建学生列表。该应用程序应具有三个功能:显示列表、添加新学生和通过 ID 号删除学生。我做到了，它运行得很好。我想请教几个问题:

1. 是否使用不当？
2. 如果有缩短代码的空间，我很乐意收到任何建议。

这是我的代码:

struct student
{
    char first_name[20];
    char last_name[20];
    char ID_NO[14];
    struct student* previous;
    struct student* next;
};


void Menu();
void Show_List(struct student*);

struct student* Add_Student(char [], char [], char [], struct student*);
struct student* Erase_Student(char [], struct student*);

void main(void)
{
    char student_first_name[20];
    char student_last_name[20];
    char personal_code[14];

    struct student* first = NULL;
    struct student* node0 = NULL;

    int x = 0;
    int opt;

    Menu();
    for(; ;)
    {
        printf("\nEnter the operation you want to do: \n");
        scanf("%d", &opt);

        switch(opt)
        {
        case 1:
            Show_List(first);           
            break;
        case 2:
            printf("\nEnter the student's first name: ");
            scanf("%s", &student_first_name);
            printf("\nEnter the student's last name: ");
            scanf("%s", &student_last_name);
            printf("\nEnter the student's personal code: ");
            scanf("%s", &personal_code);
            node0 = Add_Student(student_first_name, student_last_name, personal_code, first);
            first = node0;
            break;
        case 3:
            printf("\nEnter the code of the student you want to erase: ");
            scanf("%s", &personal_code);
            node0 = Erase_Student(personal_code, first);
            first = node0;
            break;
        default:
            printf("\nYou entered an invalid option!!! Please try again.\n");
            Menu();
            break;
        }

    }
    scanf("%d", &x);

}

void Menu()
{
    printf("\nSelect from the Menu the operation you want to execute:\n");
    printf("\n1) Show students list;");
    printf("\n2) Add a student in the list;");
    printf("\n3) Erase a student from the list.");
}

void Show_List(struct student* firstNode)
{
    struct student* firstNodeCopy = firstNode;
    int number = 0;

    if(firstNode == NULL)
        printf("\nThe list is empty.\n");

    while(firstNodeCopy)
    {
        printf("\n%d. %s ", ++number, firstNodeCopy->first_name);
        printf("%s %s\n", firstNodeCopy->last_name, firstNodeCopy->ID_NO);
        firstNodeCopy = firstNodeCopy->next;
    }
}

struct student* Add_Student(char name_1[], char name_2[], char ID[], struct student* firstNode)
{
    struct student* start = firstNode;
    struct student* last = NULL;
    struct student* addNode = (struct student*) malloc(sizeof(struct student));

    if(firstNode == NULL)
    {
        firstNode = (struct student*) malloc(sizeof(struct student));
        strcpy(firstNode->first_name, name_1);
        strcpy(firstNode->last_name, name_2);
        strcpy(firstNode->ID_NO, ID);

        firstNode->next = NULL;
        firstNode->previous = NULL;
        return firstNode;
    }
    else
    {
        strcpy(addNode->first_name, name_1);
        strcpy(addNode->last_name, name_2);
        strcpy(addNode->ID_NO, ID);

        while(start)
            {
                if(strcmp(addNode->first_name, start->first_name) > 0)
                {
                    if(start->next == NULL)
                    {
                        start->next = addNode;
                        addNode->previous = start;
                        addNode->next = NULL;
                        return firstNode;
                    }
                    else
                    {
                        last = start;
                        start = start->next;
                    }
                }

                if(strcmp(addNode->first_name, start->first_name) < 0)
                {
                    if(last == NULL)
                    {
                        addNode->next = start;
                        start->previous = addNode;
                        return addNode;
                    }
                    else
                    {
                        addNode->next = start;
                        addNode->previous = last;
                        last->next = addNode;
                        start->previous = addNode;                  
                        return firstNode;                   
                    }
                }

                if(strcmp(addNode->first_name, start->first_name) == 0)
                {
                    if(strcmp(addNode->last_name, start->last_name) < 0)
                    {
                        if(last == NULL)
                        {
                            addNode->next = start;
                            start->previous = addNode;
                            return addNode;
                        }
                        else
                        {
                            addNode->next = start;
                            addNode->previous = last;
                            last->next = addNode;
                            start->previous = addNode;                  
                            return firstNode;
                        }
                    }

                    if(strcmp(addNode->last_name, start->last_name) > 0)
                    {
                        if(start->next == NULL)
                        {
                            start->next = addNode;
                            addNode->previous = start;
                            addNode->next = NULL;
                            return firstNode;
                        }
                        else
                        {
                            last = start;
                            start = start->next;
                        }
                    }

                    if(strcmp(addNode->last_name, start->last_name) == 0)
                    {
                        if(last == NULL)
                        {
                            addNode->next = start;
                            start->previous = addNode;
                            return addNode;
                        }
                        else
                        {
                            addNode->next = start;
                            addNode->previous = last;
                            last->next = addNode;
                            start->previous = addNode;                  
                            return firstNode;
                        }
                    }
                }
            }
    }
}

struct student* Erase_Student(char ID[], struct student* firstNode)
{
    struct student* start = firstNode;
    struct student* last = NULL;

    if(start == NULL)
    {
        printf("\nThe list is empty.\n");
        return NULL;
    }
    else
    {
        while(start)
        {
            if(strcmp(ID, start->ID_NO) == 0)
            {
                if(last == NULL)
                {
                    start = start->next;
                    return start;
                }
                else
                {
                    last->next = start->next;
                    return firstNode;
                }
            }
            else
            {
                last = start;
                start = start->next;
            }
        }
        printf("\nYou entered a WRONG personal ID number to erase!!! Please try again.\n");
        return firstNode;
    }
}

Answer 1

• 添加第一个节点时发生内存泄漏，同时分配了 addNode 和 firstNode
• 当你删除一个学生时有内存泄漏，你需要free()删除的节点。
• 您应该使用函数来比较名称而不是重复的代码。类似于 int compareStudents(char * LeftFirstName, char * LeftLastName, char * RightFirstName, char * RightLastName);

除此之外，逻辑还是不错的。