# 📅 C++ Calendar Application - Complete Documentation

## Table of Contents
1. [Features](#-features)
2. [Installation](#-installation)
3. [Command Reference](#-command-reference)
4. [Technical Report](#project-report-advanced-calendar-application-in-c)
5. [System Architecture](#2-system-architecture)
6. [Key Functions](#3-deep-dive-into-key-functions)
7. [User Flow](#4-user-interaction-flowchart)
8. [Error Handling](#5-error-handling-mechanisms)
9. [Conclusion](#8-conclusion)

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## 🌟 Features
- **Interactive Calendar Display**
  - Highlight current day `[17]` and events `|19|`
  - Support for both AD and BCE dates
- **Comprehensive Event Management**
  - Add/delete events with reminders
  - View all events chronologically
- **Intuitive Navigation**
  - Month/year, daily/weekly movement
  - Quick jump to specific dates
- **Data Persistence**
  - Automatic saving/loading
  - Custom export/import functionality
- **Robust Validation**
  - Date validation
  - Error-resistant command handling

---

## 🛠️ Installation
```bash
# Compile and run
g++ main.cpp -o calendar -std=c++11 && ./calendar

---

🖥️ Usage

Navigation Commands

Key	Action	Example	Behavior
p	Previous month	p	Wraps to December at January
n	Next month	n	Wraps to January at December
s	Specific date	s 12 2024 25	Jumps to Dec 25, 2024
u	Previous week	u	Moves back 7 days
b	Next week	b	Moves forward 7 days
c	Current date	c	Returns to today

Event Commands

Key	Action	Example
a	Add event	a 15 5 2024 "Meeting"
d	Delete event	d 2 (deletes event ID 2)
l	List events	Shows all events

System Commands

Key	Action	Example
f	Export events	f events.txt
i	Import events	i backup.txt
q	Quit program	Saves before exiting

---

Visual Indicators:

• Current day always marked with [ ]
• Week navigation preserves relative day position

Special Cases

1. Leap Years:

   February 2024:
   [28] → `>` → [29] (Leap day)
   [29] → `>` → [1] (March)
   

2. BCE Dates:

   > s
   Month: 1 Year: -44 (44 BCE)
   Shows January 44 BCE with Julian calendar rules
   

Navigation Flowchart

graph TD
    A[Current View] --> B{Key Press}
    B -->|p/n| C[Month Change]
    B -->|s| D[Jump to Date]
    B -->|< > u b| E[Day Adjustment]
    C --> F[Recalculate Grid]
    D --> F
    E --> F
    F --> G[Refresh Display]

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Tips:

1. Press c to quickly return to current date
2. Combine s with no day input to view month overview
3. Week navigation (u/b) maintains same month

## ⌨️ Command Reference  
| Key | Action                  | Example Usage          |  
|-----|-------------------------|------------------------|  
| `a` | Add event               | `a → 5 16 2025 "Meeting"` |  
| `d` | Delete event            | `d → [ID]`             |  
| `f` | Save to file            | `f → events_backup.txt`|  
| `g` | Go to event             | `g → [ID]`             |  
| `q` | Quit                    | `q` (Exits program)    |  

## 📂 File Formats
### System Auto-Save File (`2.718281828459045235.txt`)
Stores events in a compact format for program reloading:
```plaintext
[YEAR] [MONTH] [DAY]
[Event Description]

Example:

2025 5 16
Team Meeting
2025 6 19
Doctor's Appointment

Custom Export Files (User-Specified)

Saved in human-readable format when using f command:

Date: [DAY]/[MONTH]/[YEAR]
Description: [Event Description]

Example:

Date: 16/5/2025
Description: Team Meeting

Date: 19/6/2025
Description: Doctor's Appointment

Key Differences:

Feature	Auto-Save Format	Custom Export Format
Structure	Raw data	Labeled fields
Delimiters	Spaces	Slashes (dates)
Readability	Machine-optimal	Human-friendly
Extension	.txt	User-defined

Technical Report: Advanced Calendar Application in C++

1. System Architecture

1.1 Class Diagram

classDiagram
    class Date{
        -int day, month, year
        -int nDay[12]
        -string months[12]
        +isLeap(int): bool
        +getDaysInMonth(): int
    }
    
    class Event{
        -string eDesc
        -Date date
        +printEvent()
        +printinFile(fstream&)
    }

    class Calendar{
        -vector<Event> events
        -fstream cFile
        +enterEvent()
        +deleteEvent()
        +printCal()
        +fileOperation()
    }
    Date <|-- Calendar
    Calendar "1" *-- "many" Event

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1.2 Program Flow

graph TD
    A[Start] --> B[Initialize Calendar]
    B --> C{Display Current Month}
    C --> D[Wait for User Input]
    D -->|Key Press| E[Process Command]
    E -->|Navigation| C
    E -->|Add Event| F[Store in Vector & File]
    E -->|Quit| G[Save All Events]

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2. Core Functionality

2.1 Date Validation (isLeap)

bool Date::isLeap(int year) {
    return (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0);
}

2.2 Calendar Rendering

Output Example:

Sun Mon Tue Wed Thu Fri Sat
          1   2   3   4   5
  6   7   8   9  10  11  12
 13 14  15  16  [17] 18 |19|

📅 Event Handling System (Enhanced)

2.3 Event Persistence

File Format:

2025 5 16
Team Meeting

The calendar now supports multiple events per day with optimized display logic and robust input handling. Key changes include:

2.4. Multi-Event Day Support

• Old Behavior: Only displayed one marker (|day|) per day regardless of event count
• New Behavior:

  // Collects ALL events for the month
  for (Event e : events) {
      if (e.matchesMonth(mon, yr)) {
          eday.push_back(e.getDay()); // Stores all event days
      }
  }
  sort(eday.begin(), eday.end()); // Ensures chronological display

  • Days with events show |day| marker whether they have 1 or 100 events
  • Event list at month bottom shows all events for highlighted days

2.5 Event Navigation

Command	Old Behavior	New Behavior
g	Broke with multi-event days	Shows target day with all events preserved
u/b (week nav)	Could skip events	Maintains correct event markers during week jumps

2.6 Edge Case Handling

Tested scenarios:

• ✅ 5+ events on a single day
• ✅ Events on month boundaries (e.g., Jan 31 + Feb 1)
• ✅ Leap day events (Feb 29)
• ✅ Empty event lists

How to Add Events:

1. Press 'a'  
2. Enter date (Day Month Year)  
3. Type event description  
4. See all events for that day marked with |day|  

Example Output:

Sun Mon Tue Wed Thu Fri Sat  
         |1|   2    3    4  
  5    6    7  [8]  |9|  10  

• |9| = Day with 1+ events
• [8] = Current day (with or without events)

3. User Interaction

graph LR
    A[Main Menu] --> B[[p/n: Change Month]]
    A --> C[[a: Add Event]]
    C --> D[Enter Date & Description]
    D --> E[Save to Vector & File]

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4 🛡️ Error Handling System

Smart Input Processing

The calendar intelligently handles user input with these protective measures:

4.1 First-Character Command Parsing

string input;
getline(cin, input);          // Captures full input line
choice = toupper(input[0]);   // Only considers first character

Behavior Examples:

Input	Effective Command	Buffer Handling
"n"	Next Month (N)	Cleans residual buffer
"next"	Next Month (N)	Auto-discards "ext"
"nn"	Next Month (N)	Ignores second 'n'
" x"	Invalid (space)	Full discard

4.2 Type Validation Upgrade

int typeValidation() {
    string input;
    getline(cin, input);
    
    // First-character priority with fallback
    if (isdigit(input[0])) {
        try {
            return stoi(input);
        } catch (...) { /* handle overflow */ }
    }
    return 0; // Unified failure case
}

4.3 Input Processing Flow

graph LR
    A[Raw Input] --> B(Extract First Char)
    B --> C{Valid Command?}
    C -->|Yes| D[Execute]
    C -->|No| E[Show Error Menu]
    D & E --> F[Auto-Clear Buffer]

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Key Design Choices:

1. Lenient Parsing:

   • "pReV" → Processes as P (Previous)
   • "aDD" → Processes as A (Add Event)

2. Silent Buffer Cleaning:

   // After every command:
   cin.ignore(numeric_limits<streamsize>::max(), '\n');

3. Visual Feedback:

   Enter Command: nextmonth
   [System]: Executing 'N' (Next Month)

Special Cases Handled:

• Leading Whitespace: " c" → Current Month (C)
• Symbolic Input: ">>" → Next Day (>)
• Empty Enter: No-op (preserves current view)

5. Visual Demonstration

![Calendar Screenshot]

• |19| = Event day
• [17] = Current day

Key Algorithms

• Zeller's Congruence for weekday calculation
• Leap year detection (including BCE dates)
• Smart date wrapping for month/year transitions

6. Conclusion

This application demonstrates:
✔ Modular OOP design
✔ Robust file persistence
✔ Intuitive keyboard controls

Future Work:

• Recurring events
• GUI interface
• Cloud synchronization

📜 MIT License