[日常] C语言的简单账户增删改查样例

最近在帮考研跨考计算机的朋友学习C语言，from zero.
用单链表实现了一个账户的管理系统。
麻雀虽小，五脏俱全。单链表的增删改查（CRUD）全在里面了，结构也很清晰，适合初学者学习链表的基本操作。

#include 
#include 
#include 

#define _CRT_SECURE_NO_DEPRECATE
#define _CRT_SECURE_NO_WARNINGS

#define BUFFER_SIZE 100
#define MAX_ACCOUNT_USERNAME_LENGTH 20
#define MAX_ACCOUNT_PASSWORD_LENGTH 20

typedef struct _account{
     
	char username[MAX_ACCOUNT_PASSWORD_LENGTH];
	char password[MAX_ACCOUNT_PASSWORD_LENGTH];
	struct _account* next;
}Account;

enum Choices{
     
    Create,Retrieve,Update,Delete,SeeAll,DeleteAll
};

Account* accoutLinkedList = NULL;

void printUsage();
void createAccount();
Account* findUsername(const char* username);
void retrieveAccount();
void updateAccount();
void deleteAccont();
void seeAllAcount();
void deleteAllAccount();

int main(int argc, char const *argv[])
{
     
    printf("Welcome to the dummy account management system.\n");
    int choice;
    while(1){
     
        system("CLS");//clear the view
        printUsage();
        scanf("%d",&choice);
        putchar('\n');
        choice --;//counting from zero
        switch(choice){
     
            case Create:
                createAccount();
                break;
            case Retrieve:
                retrieveAccount();
                break;
            case Update:
                updateAccount();
                break;
            case Delete:
                deleteAccont();
                break;
            case SeeAll:
                seeAllAcount();
                break;
            case DeleteAll:
                deleteAllAccount();
                break;
            default:
                printf("Illegal menu number!\n");
        }
        putchar('\n');
        printf("Press any key to continue.\n");
        getchar();//eat the \n
        getchar();//choke
    }
    return 0;
}


void printUsage(){
     
        printf("Key in a number to select a menu...\n"
                "1. Create a account\n"
                "2. Retrieve password with a username\n"
                "3. Update password for a username\n"
                "4. Delete a existing account from the system\n"
                "5. See all accounts in the system\n"
                "6. Delete all accounts from the system\n");
}

void createAccount(){
     
        //input
        char buffer[BUFFER_SIZE];
        char username[MAX_ACCOUNT_USERNAME_LENGTH];
        char password[MAX_ACCOUNT_PASSWORD_LENGTH];
        printf("Create a account\n");
        printf("The system won't check if the username already exists.\n");
        printf("Key in the username, max length allowed = %d.\n",MAX_ACCOUNT_USERNAME_LENGTH);
        scanf("%s",buffer);
        strncpy(username,buffer,MAX_ACCOUNT_USERNAME_LENGTH);
        printf("Key in the password for user[%s],max length allowed = %d.\n",username,MAX_ACCOUNT_PASSWORD_LENGTH );
        scanf("%s",buffer);
        strncpy(password,buffer,MAX_ACCOUNT_PASSWORD_LENGTH);

        //add
        Account *a = (Account*)malloc(sizeof(Account));
        strncpy(a->username,username,MAX_ACCOUNT_USERNAME_LENGTH);
        strncpy(a->password,password,MAX_ACCOUNT_PASSWORD_LENGTH);
        a->next = NULL;

        //insert
        Account *iter;
        if(accoutLinkedList == NULL){
     
            accoutLinkedList = a;
        }else{
     
            //iterate to the last elem
            iter = accoutLinkedList;
            while(iter->next){
     
                iter=iter->next;
            }
            //append
            iter->next = a;
        }
        printf("New account: Username[%s]->Password[%s] appended.\n",a->username,a->password );
}

Account* findUsername(const char* username){
     
    Account *iter;
    for(iter= accoutLinkedList;iter!= NULL;iter=iter->next){
     
        if(!strncmp(iter->username,username,MAX_ACCOUNT_USERNAME_LENGTH)){
     
            break;
        }
    }
    return iter;
}

void retrieveAccount(){
     
    //input
    char buffer[BUFFER_SIZE];
    printf("Retrieve a account\n");
    printf("Key in the username, max length allowed = %d.\n",MAX_ACCOUNT_USERNAME_LENGTH);
    scanf("%s",buffer);

    //find
    Account *iter = findUsername(buffer);

    if(!iter){
     
        printf("Username[%s] does not exist.\n",buffer);
        return;
    }

    printf("Username[%s] setted the password to [%s].\n",iter->username,iter->password);
}

void updateAccount(){
     
    //input
    char buffer[BUFFER_SIZE];
    printf("Update a account\n");
    printf("Key in the username, max length allowed = %d.\n",MAX_ACCOUNT_USERNAME_LENGTH);
    scanf("%s",buffer);

    //find
    Account *iter = findUsername(buffer);

    if(!iter){
     
        printf("Username[%s] does not exist.\n",buffer);
        return;
    }

    //update
    printf("Old password is [%s], key in a new one, max length allowed = %d.\n",iter->password,MAX_ACCOUNT_PASSWORD_LENGTH);
    scanf("%s",buffer);
    strncpy(iter->password,buffer,MAX_ACCOUNT_PASSWORD_LENGTH);
    printf("Username[%s] setted the password to [%s].\n",iter->username,iter->password);
}

void deleteAccont(){
     
    //input
    char buffer[BUFFER_SIZE];
    printf("Update a account\n");
    printf("Key in the username, max length allowed = %d.\n",MAX_ACCOUNT_USERNAME_LENGTH);
    scanf("%s",buffer);

    //find prev
    int isFound = 0;
    Account *prev = NULL;
    Account *iter;
    for(iter=accoutLinkedList;iter!=NULL;prev = iter,iter=iter->next){
     
        if(!strncmp(iter->username,buffer,MAX_ACCOUNT_USERNAME_LENGTH)){
     
            isFound = 1;
            break;
        }
    }

    if(!isFound){
     
         printf("Username[%s] does not exist.\n",buffer);
         return ;
    }

    if(prev){
     
        prev->next = iter->next;
    }else{
     
        accoutLinkedList = iter->next;
    }
    free(iter);
    printf("Deleted!");
}

void seeAllAcount(){
     
    const Account *iter;
    int counter = 0;
    printf("See all accounts\n");
    for(iter = accoutLinkedList;iter!=NULL;iter=iter->next){
     
        printf("Account #%d\n",counter++);
        printf("Username:%s\nPassword:%s\n\n",iter->username,iter->password);
    }
}

void deleteAllAccount(){
     
    Account *iter,*tmp;
    iter = accoutLinkedList;
    while(iter){
     
        tmp = iter;
        iter = iter->next;
        free(tmp);
    }
    accoutLinkedList = NULL;
    printf("Completed!\n");
}

一些测试

欢迎界面

Key in a number to select a menu...
1. Create a account
2. Retrieve password with a username
3. Update password for a username
4. Delete a existing account from the system
5. See all accounts in the system
6. Delete all accounts from the system

创建账户

Create a account
The system won't check if the username already exists.
Key in the username, max length allowed = 20.
sun
Key in the password for user[sun],max length allowed = 20.
114514
New account: Username[sun]->Password[114514] appended.

Press any key to continue.

获取账户密码

//存在
Retrieve a account
Key in the username, max length allowed = 20.
sun
Username[sun] setted the password to [114514].

Press any key to continue.
//不存在
Retrieve a account
Key in the username, max length allowed = 20.
otaku
Username[otaku] does not exist.

Press any key to continue.

更新账户密码

//存在
Update a account
Key in the username, max length allowed = 20.
sun
Old password is [114514], key in a new one, max length allowed = 20.
1919810
Username[sun] setted the password to [1919810].

Press any key to continue.
//不存在
Update a account
Key in the username, max length allowed = 20.
foobar
Username[foobar] does not exist.

Press any key to continue.

删除账户

//存在
Update a account
Key in the username, max length allowed = 20.
sun
Deleted!
Press any key to continue.
//不存在
Update a account
Key in the username, max length allowed = 20.
sun
Username[sun] does not exist.

Press any key to continue.

查看所有账户

See all accounts
Account #0
Username:sun
Password:114514

Account #1
Username:otaku
Password:1919810

Account #2
Username:gnuisnotunix
Password:wineisnotemulator


Press any key to continue.

删除所有账户

Completed!

Press any key to continue.