客户管理系统在C中注册客户

Question

提示是:我应该为客户管理系统编写一个用于注册客户的程序(用C编程语言)。

该方案应允许注册管理成员：

• 将客户记录(id、姓名、年龄、性别和城市)添加到文件中。
• 打印客户详细信息(ID、姓名、年龄、性别和城市)

(注:如果用户输入“男性或女性”以外的性别，程序应显示错误信息“无效输入！(性别必须为男性或女性)”，并强制用户输入正确的性别。)

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

int n_r=0;
struct customer                                                                         // using a struct will be better than an array since it
{                                                                                       // can store several data types unlike an array
    int id;
    char firstname[20];
    char lastname[20];

    int age;
    char gender[6];
    char city[20];
};

void displayMainMenu()                                                                  // print menu
{
    printf("\n -------------------------------------------------------------\n");
    printf("\n -------------Customer Management System ---------------------\n");
    printf("\n ------------------------* MAIN MENU *----------------------------\n");
    printf("\n |A/a:Enter A or a for Adding a Customer ");
    printf("\n |D/d:Enter D or d for Printing Customer Details ");
    printf("\n |E/e:Enter E or e for Exiting the Program |------------------\n");
}  

char inputAndCheck()
{
    char ch;
    while(1)
    {
        displayMainMenu();
        printf("\n Please enter your choice: ");
        scanf("%c",&ch);
        if(ch=='A'||ch=='a'||ch=='D'||ch=='d'||ch=='E'||ch=='e')
        break;
        else
        {
            printf("\n > Invalid selection! Please try again ");
        }
    }
    return ch;
}
    

int readCustomerAge()
{
    int age;
    while(1)
    {
        printf("\n Enter age: ");
        scanf("%d",&age);
        if(age>=15 && age<=90)

        break;
        else
        {
            printf("\n > Invalid selection! (Age must be between 15 and 90) ");
        }
    }

    return age;
}                                                                       

int readCustomerGender()
{
    char ch1[6];
    while(1)
    {
        printf("\n Enter gender: ");
        scanf("%s",ch1);
        if((strcmp(ch1,"male")==0)||(strcmp(ch1,"MALE")==0))
        {
            return 0;
        }
        else if((strcmp(ch1,"female")==0)||(strcmp(ch1,"FEMALE")==0))
        {
            return 1;
        }
        else{
            printf("\n > Invalid selection! (Gender must be male or female) ");
        }
    }
}

char* readCustomerCity()
{
    char c[20];
    printf("\n Enter city: ");
    scanf("%s",c);
    return c;
}

void displayCustomerDetails()
{
    FILE *fp;
    struct customer c;
    fp=fopen("customer.txt","r");
    if(fp==NULL)
    {
        printf("\n Error in opening a file.");
        exit(1);
    }
    while(fread(&c,sizeof(struct customer),1,fp))
    printf("\n Id:%d \n Name:%s %s \n Age=%d \n Gender=%s \n City=%s",c.id,c.firstname,c.lastname,c.age,c.gender,c.city);

    fclose(fp);
}

void addCustomerDetails()
{
    FILE *fp;
    struct customer c;
    char* gen;
    //char cit[30];
    if(n_r==0)
    {
        fp=fopen("customer.txt","w");
        if(fp==NULL)
        {
            printf("\n Error in opening a file.");
            exit(1);
        }
    }
    else
    {
        fp=fopen("customer.txt","a");
        if(fp==NULL)
        {
            printf("\n Error in opening a file.");
            exit(1);
        }
    }

    printf("\n Enter customer ID: ");
    scanf("%d",&c.id);
    printf("\n Enter customer first name: ");
    scanf("%s",&c.firstname);
    printf("\n Enter customer last name: ");
    scanf("%s",&c.lastname);
    c.age=readCustomerAge();
    if(readCustomerGender())
    {
        strcpy(c.gender,"Female");
    }
    else
    {
        strcpy(c.gender,"Male");
    }

    printf("\n Enter customer city: ");
    scanf("%s",&c.city);
    fwrite(&c,sizeof(struct customer),1,fp);
    fclose(fp); 
}

int main()
{
    int year;
    char ch;
    printf("\n -------------------------------------------------------------\n");
    printf("\n -------------Welcome to Customer Management System ---------------------\n");
    printf("\n > Please Enter Customer registration year (ex:2017):");
    scanf("%d",&year);
    printf("\n > How many customers do you want register in the year %d:",year);
    scanf("%d",&n_r);

    while(1)
    {
        ch=inputAndCheck();
        switch(ch)
        {
            case 'A':
            case 'a':
            addCustomerDetails();
            n_r++;
            break;

            case 'D':
            case 'd':
            displayCustomerDetails();
            break;
            
            case 'E':
            case 'e':
            printf("\n > Thank you for using Customer Management System!\n");
            printf("\n > Good Bye. \n");
            exit(0);
        }
    }

    return 0;
}

请注意，我还没有完成为程序的评论，但将继续写在我收到反馈意见。

Answer 1

域特定类型

而不是

char gender[6];

如果你想限制两个性别，你最好做一个enum。然而，这样做通常是一个糟糕的选择；相反，只需要接受一个自由字符串，而不必为M/F编写逻辑。

预先存在的文件

n_r目前唯一有用的角色似乎是决定数据库文件的写入模式。您可以完全摆脱它，并根据I/O操作自动排序写入模式。

前后换行符

在命令行接口中，更典型的做法是

printf("Foo\n");

比

printf("\nFoo");

因为--从程序的一开始--我们就假设得到一个空行，所以做第二行是没有意义的。另一个原因是，某些缓存逻辑依赖后缀换行符，而不是前缀换行符，以知道何时写入流。

inputAndCheck

您基本上是一次检查这个逻辑，一次检查有效的选择字符，另一次实际注意选择。这样做一次而不是tolower()，这样您只需要检查一个值。

验证循环

scanf已经..。很多问题。例如，它污染了stdin缓冲区，因此很难从错误(例如，有人输入文本而不是整数)中恢复。

一个常见的解决方法是用fgets/sscanf对替换它。

关注点分离

displayCustomerDetails实际上做了两件事--从文件中读取，并显示给stdout。你应该把这个分开。同样适用于addCustomerDetails。

未用输入

您要求--而且完全忽略--注册年份的输入；而n_r的输入既令人困惑，也没有正确地使用。你可以把这两样都处理掉。

超支

当扫描到固定缓冲区中的字符串时，关键是要告诉输入函数缓冲区大小，这样就不会出现溢出。C特别容易受到缓冲区溢出崩溃和安全漏洞的影响。

Backus-Naur

 |E/e

在格式化方面有点奇怪。熟悉命令行接口的用户将管道理解为两个选项之间的“或”；因此，在这里将其视为可视分隔符有点令人不快。EBNF建议使用E|e。

建议

此代码提供了一种处理(大部分)上述问题的方法：

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

static int n_r = 0;

typedef enum {
    MALE = 0,
    FEMALE = 1
} gender;

typedef struct tag_customer
{
    unsigned id;
    char firstname[20];
    char lastname[20];

    unsigned age;
    gender gender;
    char city[20];
} customer;

static void displayMainMenu()
{
    puts(
          "-------------------------------------------------------------"
        "\n-------------Customer Management System ---------------------"
        "\n------------------------* MAIN MENU *------------------------"
        "\n A|a: Add a Customer"
        "\n D|d: Print Customer Details"
        "\n E|e: Exit"
    );
}

static void scanLoop(const char *prompt, const char *fmt, void *dest)
{
    char buffer[80];
    int fields;
    do
    {
        printf(prompt);
        if (!fgets(buffer, sizeof(buffer), stdin))
        {
            perror("I/O error on stdin");
            exit(1);
        }

        fields = sscanf(buffer, fmt, dest);
    } while (fields != 1);
}

static char menuChoice()
{
    displayMainMenu();
    char choice;
    scanLoop("Please enter your choice: ", "%c", &choice);
    return tolower(choice);
}

static unsigned readCustomerAge()
{
    while (true)
    {
        unsigned age;
        scanLoop("Enter age: ", "%u", &age);
        if (age >= 15 && age <= 90)
            return age;
        puts("Invalid selection! (Age must be between 15 and 90)");
    }
}

static gender readCustomerGender()
{
    char buffer[10];
    while (true)
    {
        scanLoop("Enter gender (male|female): ", "%9s", buffer);

        for (char *p = buffer; *p; p++)
            *p = tolower(*p);

        if (!strcmp(buffer, "male"))
            return MALE;
        if (!strcmp(buffer, "female"))
            return FEMALE;

        puts("Invalid selection!");
    }
}

static void displayCustomer(const customer *c)
{
    printf(
        "Id: %u"
        "\nName: %s %s"
        "\nAge: %u"
        "\nGender: %s"
        "\nCity: %s"
        "\n",
        c->id, c->firstname, c->lastname, c->age,
        c->gender == MALE ? "male" : "female",
        c->city
    );
}

static void readCustomers(const char *filename)
{
    FILE *fp;
    customer c;
    fp = fopen(filename, "r");
    if (fp == NULL)
    {
        perror("Error opening file for customer display");
        exit(1);
    }

    while (fread(&c, sizeof(customer), 1, fp))
        displayCustomer(&c);

    fclose(fp);
}

static void scanCustomer(customer *c)
{
    scanLoop("Enter customer ID: ", "%u", &c->id);
    scanLoop("Enter customer first name: ", "%20s", c->firstname);
    scanLoop("Enter customer last name: ", "%20s", c->lastname);

    c->age = readCustomerAge();
    c->gender = readCustomerGender();

    scanLoop("Enter city: ", "%20s", c->city);
}

static void addCustomer(const char *filename)
{
    const char *mode;
    if (n_r == 0)
        mode = "w";
    else mode = "a";

    FILE *fp = fopen(filename, mode);
    if (fp == NULL)
    {
        perror("Error in opening customer file for writing");
        exit(1);
    }

    customer c;
    scanCustomer(&c);
    fwrite(&c, sizeof(customer), 1, fp);
    fclose(fp);
}

static unsigned readYear()
{
    unsigned year;
    while (true)
    {
        scanLoop("Please Enter Customer registration year (ex:2017): ", "%u", &year);
        if (year >= 2000 && year <= 2500)
            return year;
        puts("Year out of range");
    }
}

int main()
{
    printf(
          "------------------------------------------------------------------------"
        "\n-------------Welcome to Customer Management System ---------------------"
        "\n"
        "\n"
    );

    readYear();

    while (true)
    {
        switch (menuChoice())
        {
            case 'a':
                addCustomer("customer.txt");
                n_r++;
                break;

            case 'd':
                readCustomers("customer.txt");
                break;

            case 'e':
                puts(
                    "Thank you for using Customer Management System!"
                    "\nGoodbye."
                );
                return 0;

            default:
                puts("Invalid selection! Please try again.");
        }
    }
}