实现线性表的插入、删除、求表长、查找给定值e、查找第i个位置元素 等基本操作，要求编写的程序以菜单方式工作；

要实现线性表的基本操作，你可以使用数组或链表数据结构来存储数据。这里我将以链表为例，因为链表非常适合动态添加和删除元素。以下是一个简单的C语言程序，它实现了上述功能：

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

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

// 初始化链表头指针
Node* head = NULL;

// 插入元素到链表末尾
void insert(int value) {
    Node* newNode = (Node*)malloc(sizeof(Node));
    if (!newNode) {
        printf("Memory allocation failed.\n");
        return;
    }
    newNode->data = value;
    newNode->next = NULL;

    if (head == NULL) {
        head = newNode;
    } else {
        Node* temp = head;
        while (temp->next != NULL) {
            temp = temp->next;
        }
        temp->next = newNode;
    }
}

// 删除指定值的节点（如果存在）
void delete(int value) {
    Node* temp = head, *prev = NULL;

    if (temp != NULL && temp->data == value) {
        head = temp->next;
        free(temp);
        return;
    }

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

    if (temp == NULL) {
        printf("Value not found in the list.\n");
        return;
    }
    prev->next = temp->next;
    free(temp);
}

// 求表长
int length() {
    int count = 0;
    Node* temp = head;
    while (temp != NULL) {
        count++;
        temp = temp->next;
    }
    return count;
}

// 查找给定值 e
Node* find(int value) {
    Node* temp = head;
    while (temp != NULL) {
        if (temp->data == value) {
            return temp;
        }
        temp = temp->next;
    }
    return NULL;
}

// 查找第 i 个元素
Node* find_at_index(int index) {
    if (index >= 0 && index < length()) {
        Node* temp = head;
        for (int i = 0; i < index; i++) {
            temp = temp->next;
        }
        return temp;
    } else {
        printf("Index out of range.\n");
        return NULL;
    }
}

// 主菜单
void menu() {
    while (true) {
        printf("\n1. Insert\n2. Delete\n3. Check Length\n4. Find Value\n5. Find Element at Index\n6. Exit\n");
        int choice;
        scanf("%d", &choice);

        switch (choice) {
        case 1:
            int value;
            printf("Enter value to insert: ");
            scanf("%d", &value);
            insert(value);
            break;
        case 2:
            int value_to_delete;
            printf("Enter value to delete: ");
            scanf("%d", &value_to_delete);
            delete(value_to_delete);
            break;
        case 3:
            printf("List length: %d\n", length());
            break;
        case 4:
            int search_value;
            printf("Search value: ");
            scanf("%d", &search_value);
            Node* result = find(search_value);
            if (result) {
                printf("Found at position: %ld\n", (long)(result - head + 1));
            } else {
                printf("Value not found.\n");
            }
            break;
        case 5:
            int index;
            printf("Enter index: ");
            scanf("%d", &index);
            Node* result = find_at_index(index);
            if (result) {
                printf("Element at index: %d\n", result->data);
            } else {
                printf("Invalid index.\n");
            }
            break;
        case 6:
            printf("Exiting...\n");
            exit(0);
        default:
            printf("Invalid choice. Try again.\n");
        }
    }
}

int main() {
    menu();
    return 0;
}

这个程序首先定义了链表节点结构，然后创建了一个主菜单函数，根据用户的输入执行相应的操作。每个操作都有相应的函数来处理实际的操作，比如插入、删除、查找等。