通过键盘读取元素建立单链表；指定一个元素，在此元素之前插入一个新元素；指定一个元素，删除此元素。写一串c语言代码实现以上内容

以下是C语言代码，实现了通过键盘读取元素构建单链表、在指定位置插入新元素以及删除指定元素的功能：

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

// 定义链表节点结构体
typedef struct Node {
    int data;
    struct Node* next;
} Node;

// 创建新节点并分配内存
Node* createNode(int value) {
    Node* newNode = (Node*)malloc(sizeof(Node));
    if (newNode) {
        newNode->data = value;
        newNode->next = NULL;
    } else {
        printf("Memory allocation failed.\n");
        exit(1);
    }
    return newNode;
}

// 在链表前插入新元素
void insertAtBeginning(Node** head, int value) {
    Node* newNode = createNode(value);
    newNode->next = *head;
    *head = newNode;
}

// 删除指定元素
void deleteElement(Node** head, int target) {
    Node* temp = *head;
    Node* prev = NULL;

    while (temp && temp->data != target) {
        prev = temp;
        temp = temp->next;
    }

    if (temp) {
        if (prev) {
            prev->next = temp->next;
        } else {
            *head = temp->next;
        }
        free(temp); // 释放已删除节点的内存
    } else {
        printf("Element not found in the list.\n");
    }
}

// 打印链表
void printList(Node* head) {
    Node* temp = head;
    while (temp) {
        printf("%d -> ", temp->data);
        temp = temp->next;
    }
    printf("NULL\n");
}

int main() {
    Node* head = NULL;

    while (1) {
        int choice, value;
        printf("\n1. Insert at beginning\n2. Delete element\n3. Exit\n");
        scanf("%d", &choice);

        switch (choice) {
            case 1:
                printf("Enter value to insert: ");
                scanf("%d", &value);
                insertAtBeginning(&head, value);
                break;
            case 2:
                printf("Enter value to delete: ");
                scanf("%d", &value);
                deleteElement(&head, value);
                break;
            case 3:
                if (head)
                    printList(head);
                printf("Leaving program...\n");
                exit(0);
            default:
                printf("Invalid choice.\n");
        }
    }

    return 0;
}