用C语言编制一个能演示执行集合的交、并和差运算的程序。集合元素用小写英文字母，执行各种操作应以对话方式执行。算法要点：利用单链表表示集合，理解好三种运算的含义

好的，以下是用C语言编制的演示执行集合的交、并和差运算的程序：

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

//定义单链表结构体
struct node {
    char data;
    struct node *next;
};

//创建单链表
struct node *create() {
    struct node *head;
    head = (struct node*)malloc(sizeof(struct node));
    head->next = NULL;
    return head;
}

//添加元素到单链表中
void add_element(struct node *head, char element) {
    struct node *p;
    p = (struct node*)malloc(sizeof(struct node));
    p->data = element;
    p->next = head->next;
    head->next = p;
}

//删除单链表中的元素
void delete_element(struct node *head, char element) {
    struct node *p, *q;
    p = head->next;
    q = head;
    while(p != NULL) {
        if(p->data == element) {
            q->next = p->next;
            free(p);
            p = q->next;
        } else {
            q = p;
            p = p->next;
        }
    }
}

//判断元素是否在单链表中
int is_in_set(struct node *head, char element) {
    struct node *p;
    p = head->next;
    while(p != NULL) {
        if(p->data == element) {
            return 1;
        }
        p = p->next;
    }
    return 0;
}

//打印单链表
void print_set(struct node *head) {
    struct node *p;
    p = head->next;
    printf("{");
    while(p != NULL) {
        printf("%c ", p->data);
        p = p->next;
    }
    printf("}\n");
}

//求集合的交集
void intersect(struct node *set1, struct node *set2) {
    struct node *p;
    p = set1->next;
    while(p != NULL) {
        if(!is_in_set(set2, p->data)) {
            delete_element(set1, p->data);
        }
        p = p->next;
    }
}

//求集合的并集
void union_set(struct node *set1, struct node *set2) {
    struct node *p;
    p = set2->next;
    while(p != NULL) {
        if(!is_in_set(set1, p->data)) {
            add_element(set1, p->data);
        }
        p = p->next;
    }
}

//求集合的差集
void difference(struct node *set1, struct node *set2) {
    struct node *p;
    p = set2->next;
    while(p != NULL) {
        if(is_in_set(set1, p->data)) {
            delete_element(set1, p->data);
        }
        p = p->next;
    }
}

int main() {
    struct node *set1, *set2;
    char element;
    int choice;
    set1 = create();
    set2 = create();

    //添加元素到集合1中
    printf("请输入集合1中的元素，按回车键结束：\n");
    while((element = getchar()) != '\n') {
        add_element(set1, element);
    }
    getchar();

    //添加元素到集合2中
    printf("请输入集合2中的元素，按回车键结束：\n");
    while((element = getchar()) != '\n') {
        add_element(set2, element);
    }

    while(1) {
        //打印菜单
        printf("请选择要执行的操作：\n");
        printf("1. 求集合的交集\n");
        printf("2. 求集合的并集\n");
        printf("3. 求集合的差集\n");
        printf("4. 退出程序\n");

        //读入选择
        scanf("%d", &choice);

        switch(choice) {
            case 1:
                intersect(set1, set2);
                printf("集合1和集合2的交集为：");
                print_set(set1);
                break;
            case 2:
                union_set(set1, set2);
                printf("集合1和集合2的并集为：");
                print_set(set1);
                break;
            case 3:
                difference(set1, set2);
                printf("集合1和集合2的差集为：");
                print_set(set1);
                break;
            case 4:
                exit(0);
            default:
                printf("输入有误，请重新输入！\n");
        }
    }

    return 0;
}

运行程序后，按照提示依次输入集合1和集合2中的元素，然后选择要执行的操作即可进行交、并和差运算，并输出结果。