C語言更新迴圈連結串列中的資料項程式

建立一個迴圈連結串列，並更新迴圈連結串列中的資料項的範例程式，將以下程式碼儲存到一個原始檔中：update_item_in_circular_linked_list.c， 如下所示 -

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

struct node {
    int data;
    struct node *next;
};

struct node *head = NULL;
struct node *current = NULL;

//insert link at the first location
void insert(int data) {
    // Allocate memory for new node;
    struct node *link = (struct node*) malloc(sizeof(struct node));

    link->data = data;
    link->next = NULL;

    // If head is empty, create new list
    if (head == NULL) {
        head = link;
        head->next = link;
        return;
    }

    current = head;

    // move to the end of the list
    while (current->next != head)
        current = current->next;

    // Insert link at the end of the list
    current->next = link;

    // Link the last node back to head
    link->next = head;

}

void update_data(int old, int new) {
    int pos = 0;

    if (head == NULL) {
        printf("Linked List not initialized\n");
        return;
    }

    current = head;

    while (current->next != head) {
        if (current->data == old) {
            current->data = new;
            printf("\n%d found at position %d, replaced with %d\n", old, pos, new);
            return;
        }
        current = current->next;
        pos++;
    }

    if (current->data == old) {
        current->data = new;
        printf("\n%d found at position %d, replaced with %d\n", old, pos, new);
        return;
    }

    printf("%d does not exist in the list\n", old);
}


//display the list
void printList() {
    struct node *ptr = head;

    printf("\n[head] =>");

    //start from the beginning
    while (ptr->next != head) {
        printf(" %d =>", ptr->data);
        ptr = ptr->next;
    }

    printf(" %d =>", ptr->data);
    printf(" [head]\n");
}

int main() {
    insert(10);
    insert(20);
    insert(30);
    insert(40);
    insert(50);
    insert(60);

    printList();
    update_data(50, 555);
    printList();

    return 0;
}

執行上面程式，得到以下結果 -

[head] => 10 => 20 => 30 => 40 => 50 => 60 => [head]

50 found at position 4, replaced with 555

[head] => 10 => 20 => 30 => 40 => 555 => 60 => [head]