C语言管理员和用户登录系统

实现一个C语言管理员和用户登录系统的基本步骤如下：

1. 定义用户和管理员的结构体，包括用户名、密码等信息。

2. 定义一个函数用于验证用户输入的用户名和密码是否正确，可以使用数组、文件等方式存储已注册的用户信息。

3. 定义一个函数用于管理员登录，管理员可以添加、删除、修改用户信息等操作。

4. 在主函数中，根据用户选择调用相应的函数。

下面是一个简单的代码示例：

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

#define MAX_USERS 100

struct User {
    char username[20];
    char password[20];
};

struct Admin {
    char username[20];
    char password[20];
};

struct User users[MAX_USERS];
struct Admin admin = {"admin", "admin"};

int num_users = 0;

int validate_user(char* username, char* password) {
    for (int i = 0; i < num_users; i++) {
        if (strcmp(users[i].username, username) == 0 &&
            strcmp(users[i].password, password) == 0) {
            return 1;
        }
    }
    return 0;
}

int admin_login() {
    char username[20], password[20];
    printf("Enter admin username: ");
    scanf("%s", username);
    printf("Enter admin password: ");
    scanf("%s", password);
    if (strcmp(admin.username, username) == 0 &&
        strcmp(admin.password, password) == 0) {
        return 1;
    }
    printf("Invalid admin username or password\n");
    return 0;
}

void add_user() {
    char username[20], password[20];
    printf("Enter username: ");
    scanf("%s", username);
    printf("Enter password: ");
    scanf("%s", password);
    strcpy(users[num_users].username, username);
    strcpy(users[num_users].password, password);
    num_users++;
    printf("User added successfully\n");
}

void delete_user() {
    char username[20];
    printf("Enter username to delete: ");
    scanf("%s", username);
    for (int i = 0; i < num_users; i++) {
        if (strcmp(users[i].username, username) == 0) {
            for (int j = i; j < num_users - 1; j++) {
                users[j] = users[j+1];
            }
            num_users--;
            printf("User deleted successfully\n");
            return;
        }
    }
    printf("User not found\n");
}

void modify_user() {
    char username[20], new_password[20];
    printf("Enter username to modify: ");
    scanf("%s", username);
    for (int i = 0; i < num_users; i++) {
        if (strcmp(users[i].username, username) == 0) {
            printf("Enter new password: ");
            scanf("%s", new_password);
            strcpy(users[i].password, new_password);
            printf("User modified successfully\n");
            return;
        }
    }
    printf("User not found\n");
}

int main() {
    int choice;
    char username[20], password[20];
    while (1) {
        printf("1. Login\n");
        printf("2. Admin login\n");
        printf("3. Exit\n");
        printf("Enter choice: ");
        scanf("%d", &choice);
        switch (choice) {
            case 1:
                printf("Enter username: ");
                scanf("%s", username);
                printf("Enter password: ");
                scanf("%s", password);
                if (validate_user(username, password)) {
                    printf("Login successful\n");
                } else {
                    printf("Invalid username or password\n");
                }
                break;
            case 2:
                if (admin_login()) {
                    printf("1. Add user\n");
                    printf("2. Delete user\n");
                    printf("3. Modify user\n");
                    printf("Enter choice: ");
                    scanf("%d", &choice);
                    switch (choice) {
                        case 1:
                            add_user();
                            break;
                        case 2:
                            delete_user();
                            break;
                        case 3:
                            modify_user();
                            break;
                        default:
                            printf("Invalid choice\n");
                    }
                }
                break;
            case 3:
                return 0;
            default:
                printf("Invalid choice\n");
        }
    }
    return 0;
}