Exercise C: Building a simple phonebook application

One of the best ways to learn C language programming is to practice it. This article will take you step through a project I recently completed: a simple phone book application. This app demonstrates file processing and basic data management in C, allowing you to add, view, and delete contacts.

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Detailed code explanation

Here is the complete code:

 <code class="language-c">#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，让我们创建一个新联系人：\n"); printf("请输入联系人的姓名：\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("请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("打开电话簿失败。"); 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("打开文件失败。"); 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。"); }</string.h></stdio.h></code>

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Project Features

This program implements three core functions:

1. Add a contact:
   • Allows users to enter their name and phone number.
   • Store contact information in a file named phonebook.txt .
2. View contact:
   • Read and display all contact information stored in the phonebook.txt file.
3. Delete a contact:
   • Delete the contact based on the name entered by the user.
   • Filter out deleted contacts by creating temporary files and replace the original files.

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Learning gains

Through this exercise, I consolidated the following C language knowledge:

1. File processing: Proficient in using fopen , fclose and other file operation functions, and handle the failure of file opening.
2. String operation: Use functions such as strcmp and sscanf to compare and parse strings.
3. Basic Data Management: Learn how to store and manage data in simple text files, and update file content by creating temporary files.

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Code Testing

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

 <code class="language-bash">gcc -o phonebook phonebook.c</code>

2. Run the compiled program:

 <code class="language-bash">./phonebook</code>

3. Follow the on-screen prompts to add, view, or delete contacts.
4. Open the phonebook.txt file to verify that the data is stored correctly.

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Future improvements

This program is a good start and the following improvements can be considered in the future:

1. Enter Verification: Verify the validity of the phone number (for example, including only numbers) to prevent duplicate names.
2. User interface improvement: Provides clearer prompts, allowing input of names containing multiple words (using fgets instead of scanf ).
3. Enhanced file processing: Consider data encryption for improved security, using more structured file formats such as CSV or JSON.
4. Advanced Features: Add search function to sort contacts alphabetically.

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Summarize

This exercise helped me understand the C language file processing and basic data management in the basics. This is a simple but practical program that can serve as the basis for more complex projects. If you are a beginner in C language, you highly recommend giving it a try! This is an interesting and rewarding learning process.

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