Practicing C: Building a Simple Phonebook Application

One of the best ways to learn C programming is through practical exercises. This article will take you step-by-step through a project I recently completed: creating a simple phone book application. This program allows you to add, view, and delete contacts and demonstrates file handling and basic data management in C.

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Detailed code explanation

Here is the complete code for the phone book application:

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

// 函数声明
void addContact(char name[], char number[]);
void viewContacts();
void deleteContact(char name[]);

int main() {
    int choice;
    char name[20];
    char number[20];

    printf("-- 欢迎使用您的电话簿！ -- \n");

    do {
        // 显示菜单
        printf("\n您想执行什么操作？\n");
        printf("1. 创建新联系人\t 2. 查看电话簿\t 3. 删除联系人\t 4. 退出\n");
        scanf("%d", &choice);

        switch (choice) {
            case 1:
                // 添加新联系人
                printf("很好，让我们创建一个新的联系人：\n");
                printf("输入联系人的姓名：\n");
                scanf("%s", name);
                printf("现在输入电话号码：\n");
                scanf("%s", number);
                addContact(name, number);
                break;
            case 2:
                // 查看电话簿
                printf("这是您的电话簿：\n");
                viewContacts();
                break;
            case 3:
                // 删除联系人
                printf("输入要删除的联系人的姓名：\n");
                scanf("%s", name);
                deleteContact(name);
                break;
        }
    } while (choice != 4); // 循环直到用户选择“退出”

    return 0;
}

// 向电话簿添加联系人的函数
void addContact(char name[], char number[]) {
    FILE *pFile;
    pFile = fopen("Phonebook.txt", "a");
    if (pFile == NULL) {
        printf("打开电话簿时出错。");
        return;
    }
    fprintf(pFile, "姓名: %s \t 电话: %s\n", name, number);
    printf("联系人已创建！\n");
    fclose(pFile);
}

// 查看电话簿中所有联系人的函数
void viewContacts() {
    char fileContent[200];
    FILE *pFile;
    pFile = fopen("Phonebook.txt", "r");

    while (fgets(fileContent, sizeof(fileContent), pFile)) {
        printf("\n%s", fileContent);
    }

    fclose(pFile);
}

// 从电话簿中删除联系人的函数
void deleteContact(char name[]) {
    FILE *pFile, *pTrash;
    char line[200], contactName[20], contactNumber[20];

    pFile = fopen("Phonebook.txt", "r");
    pTrash = fopen("Trash.txt", "w");

    if (pFile == NULL || pTrash == NULL) {
        printf("打开文件时出错。");
        return;
    }

    while (fgets(line, sizeof(line), pFile)) {
        sscanf(line, "姓名: %s \t 电话: %s\n", contactName, contactNumber);
        if (strcmp(name, contactName) != 0) {
            fputs(line, pTrash);
        }
    }

    fclose(pFile);
    fclose(pTrash);

    // 将旧的电话簿替换为更新后的版本
    remove("Phonebook.txt");
    rename("Trash.txt", "Phonebook.txt");
    printf("联系人已删除。");
}

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Program functions

This program implements three key functions:

1. Add contact:

   • Allow users to enter name and phone number.
   • Store contacts in a file called Phonebook.txt.

2. View contact:

   • Read and display all contacts stored in Phonebook.txt.

3. Delete contact:

   • Delete contacts based on the name entered by the user.
   • Create a temporary file to filter out deleted contacts and then replace the original file.

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Key knowledge gained from this exercise

1. File processing in C language:

   • Use fopen, fclose and file operation functions.
   • Handle errors when a file cannot be opened or accessed.

2. String processing:

   • Use functions such as strcmp and sscanf for string comparison and parsing.

3. Basic data management:

   • Store and organize data in simple text files.
   • Replace or update file contents by creating temporary files.

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How to test code

1. Copy the code into a .c file and compile it with a C compiler (e.g. gcc):

gcc -o phonebook phonebook.c

2. Run the compiled program:

./phonebook

3. Follow the on-screen instructions to add, view, or delete contacts.
4. Open Phonebook.txt to verify that the data is stored as expected.

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Potential improvements

This program is a great starting point, but here are some improvements you can try:

1. Input verification:

   • Make sure the phone number is valid (i.e. only numeric characters).
   • Prevent duplicate names from appearing in the phone book.

2. Improved UI:

   • Provide more detailed instructions.
   • Using fgets instead of scanf allows the use of multi-word names.

3. Enhanced file handling:

   • Encrypt data for security.
   • Use a structured format (such as CSV or JSON).

4. Advanced features:

   • Implement search function to quickly find contacts.
   • Sort phone book alphabetically.

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Summary

This exercise helped me strengthen my understanding of file processing and basic data management in C language. It's a simple yet practical program that can serve as a building block for more complex projects. If you're new to C, give it a try - it's a fun and rewarding way to practice programming!

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