📞 International Call Billing System

A C-based international call billing manager with integrated Python data visualization. The system lets you track, manage, and analyze customer call data through a terminal menu, and generates Matplotlib charts for usage and revenue insights.

Made by Group-12 | Languages: C · Python

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📁 Project Structure

├── billing_system.c       # Core C program — all billing logic & menu
├── analyze_customers.py   # Python script — Pandas + Matplotlib charts
└── customers.csv          # Auto-generated data file (created on Save)

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⚙️ Features

C Billing System (billing_system.c)

• Add Customer — Enter name, international phone number, and call usage in minutes; bill is auto-calculated based on country code
• View All Customers — Tabular display with name, phone, usage, bill (Rs), and user type
• Search Customer — Lookup by phone number
• Modify Record — Update a customer's usage and recalculate bill (with confirmation)
• Delete Record — Remove a customer entry (with confirmation)
• Save to CSV — Exports all records to customers.csv
• Show Graph — Saves CSV then launches the Python visualization script
• Show Statistics — Displays total customers, average usage, average bill, and top customer
• Sort Customers — Sort by Name (A–Z) or Usage (High to Low) using qsort
• Export Single Customer — Saves one customer's details to a .txt file

Python Visualization (analyze_customers.py)

• Bar Chart — Customer count per user type (Very Low / Low / Moderate / High / Very High)
• Pie Chart — Revenue share (in Rs) broken down by user type

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🌐 International Call Rates

Country Code	Country	Rate (Rs/min)
+91	India	0.10
+1	USA / Canada	7.00
+44	UK	8.50
+61	Australia	9.00
+81	Japan	10.00
+49	Germany	8.00
Other	Default	12.00

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👤 User Type Classification

Usage (minutes)	User Type
< 100	Very Low
100 – 300	Low
301 – 500	Moderate
501 – 1000	High
> 1000	Very High

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🚀 How to Run

Prerequisites

• GCC compiler
• Python 3.x with pandas and matplotlib

pip install pandas matplotlib

Compile & Run the C Program

gcc billing_system.c -o billing_system
./billing_system        # Linux / macOS
billing_system.exe      # Windows

Run the Python Visualizer Separately (optional)

python analyze_customers.py

Note: Make sure customers.csv exists (use menu option 6 – Save to CSV first) before running the visualizer, or select option 7 – Show Graph directly from the menu which saves and launches it automatically.

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📋 Phone Number Format

Phone numbers must follow the format +CCXXXXXXXXXX where CC is the country code:

+911234567890   ✅ Valid (India)
+14155552671    ✅ Valid (USA)
1234567890      ❌ Invalid (missing +)

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📊 Sample CSV Output

Name,Phone,Usage,Bill_INR,User_Type
Alice,+911234567890,250.0,25.00,Low
Bob,+14155552671,800.0,5600.00,High
Charlie,+447700900123,150.0,1275.00,Low

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🛠️ Known Issues

• analyze_customers.py contains an unresolved Git merge conflict marker (<<<<<<< HEAD / >>>>>>>). Remove the duplicate block and conflict markers before running.
• The program supports up to 100 customers in memory at a time.

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📄 License

This project was built for academic purposes. Feel free to use or modify it for learning.