用c写一个单链表创建，增删改查

以下是使用C语言实现单链表的代码，包括创建、增加节点、删除节点和查找节点等功能：

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

//定义单链表节点的结构体
struct Node {
    int data;
    struct Node* next;
}; 

//单链表头节点
struct Node* head = NULL;

//创建新节点并添加到单链表尾部
void addNode(int newData) {
    struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
    newNode->data = newData;
    newNode->next = NULL;    
    if(head == NULL) {
        head = newNode;
        return;
    }
    struct Node* current = head;
    while(current->next != NULL) {
        current = current->next;
    }
    current->next = newNode;
}

//删除指定值的节点
void deleteNode(int keyData) {
    struct Node* current = head;
    struct Node* previous = NULL;
    while(current != NULL && current->data != keyData) {
        previous = current;
        current = current->next;
    }
    if(current == NULL) {
        printf("Node not found in the list!\n");
        return;
    }
    if(current == head) {
        head = current->next;
    } else {
        previous->next = current->next;
    }
    free(current);
}

//修改指定节点的值
void updateNode(int keyData, int newData) {
    struct Node* current = head;
    while(current != NULL && current->data != keyData) {
        current = current->next;
    }
    if(current == NULL) {
        printf("Node not found in the list!\n");
        return;
    }
    current->data = newData;
}

//查找节点
struct Node* searchNode(int keyData) {
    struct Node* current = head;
    while(current != NULL && current->data != keyData) {
        current = current->next;
    }
    if(current == NULL) {
        printf("Node not found in the list!\n");
        return NULL;
    }
    return current;
}

//输出单链表中的所有节点
void printList() {
    struct Node* current = head;
    while(current != NULL) {
        printf("%d ", current->data);
        current = current->next;
    }
    printf("\n");
}

int main() {
    //测试代码
    addNode(2);
    addNode(4);
    addNode(6);
    printList();
    
    deleteNode(4);
    printList();
    
    updateNode(6, 8);
    printList();
    
    searchNode(6);
    
    return 0;
}