Practicing C: Building a Simple Phonebook Application

If you're learning C programming, practical exercises can be the best way to solidify your skills. In this post, I'll walk you through a project I worked on recently: creating a simple phonebook application. This program allows you to add, view, and delete contacts, demonstrating file handling and basic data management in C.

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Code Walkthrough

Here's the complete code for the phonebook application:

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

// Function declarations
void addContact(char name[], char number[]);
void viewContacts();
void deleteContact(char name[]);

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

    printf("-- Welcome to your phonebook! -- \n");

    do {
        // Display menu
        printf("\nWhat operation would you like to perform?\n");
        printf("1. Create a new contact\t 2. View your phonebook\t 3. Delete a contact\t 4. Exit\n");
        scanf("%d", &choice);

        switch (choice) {
            case 1:
                // Adding a new contact
                printf("Great, let's create a new contact: \n");
                printf("Enter the contact's name:\n");
                scanf("%s", name);
                printf("Now enter the phone number:\n");
                scanf("%s", number);
                addContact(name, number);
                break;
            case 2:
                // Viewing the phonebook
                printf("Here is your phonebook: \n");
                viewContacts();
                break;
            case 3:
                // Deleting a contact
                printf("Write the name of the contact you want to delete:\n");
                scanf("%s", name);
                deleteContact(name);
                break;
        }
    } while (choice != 4); // Loop until the user selects "Exit"

    return 0;
}

// Function to add a contact to the phonebook
void addContact(char name[], char number[]) {
    FILE *pFile;
    pFile = fopen("Phonebook.txt", "a");
    if (pFile == NULL) {
        printf("Error opening the phonebook.");
        return;
    }
    fprintf(pFile, "Name: %s \t Number: %s\n", name, number);
    printf("The contact has been created! \n");
    fclose(pFile);
}

// Function to view all contacts in the phonebook
void viewContacts() {
    char fileContent[200];
    FILE *pFile;
    pFile = fopen("Phonebook.txt", "r");

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

    fclose(pFile);    
}

// Function to delete a contact from the phonebook
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("Error opening the file.");
        return;
    }

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

    fclose(pFile);
    fclose(pTrash);

    // Replace the old phonebook with the updated version
    remove("Phonebook.txt");
    rename("Trash.txt", "Phonebook.txt");
    printf("The contact has been deleted.");
}

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Features of the Program

This program implements three key functionalities:

1. Add Contacts:

   • Allows the user to input a name and a phone number.
   • Stores the contact in a file named Phonebook.txt.

2. View Contacts:

   • Reads and displays all the contacts stored in Phonebook.txt.

3. Delete Contacts:

   • Removes a contact based on the name entered by the user.
   • Creates a temporary file to filter out the deleted contact, then replaces the original file.

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Key Learnings from This Exercise

1. File Handling in C:

   • Using fopen, fclose, and file manipulation functions.
   • Handling errors when files cannot be opened or accessed.

2. Working with Strings:

   • Using functions like strcmp and sscanf for string comparisons and parsing.

3. Basic Data Management:

   • Storing and organizing data in a simple text file.
   • Replacing or updating file contents by creating temporary files.

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How to Test the Code

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

   gcc -o phonebook phonebook.c

1. Run the compiled program:

   ./phonebook

1. Follow the on-screen instructions to add, view, or delete contacts.

2. Open Phonebook.txt to verify that the data is being stored as expected.

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Potential Enhancements

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

1. Input Validation:

   • Ensure phone numbers are valid (e.g., only numeric characters).
   • Prevent duplicate names in the phonebook.

2. Improved User Interface:

   • Provide more detailed instructions.
   • Allow multi-word names using fgets instead of scanf.

3. Enhanced File Handling:

   • Encrypt data for security.
   • Use a structured format (e.g., CSV or JSON).

4. Advanced Features:

   • Implement a search functionality to find contacts quickly.
   • Sort the phonebook alphabetically.

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Final Thoughts

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