ConsolePad

A console-based text editor written in C++ that runs entirely inside a Windows terminal. Built as a data-structures deep-dive: every core feature — editing, search, and word prediction — is backed by a custom data structure rather than the standard library.

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Features

Feature	Detail
2-D linked-list document model	Every character lives in a doubly-linked grid. Horizontal links connect characters within a line; vertical links connect the same column position across lines.
Operation-based undo / redo	Up to 50 operations. Each record stores only the delta (character + position), not a document snapshot.
Trie-powered full-text search	N-Ary trie (26 children per node) indexes every word in the document. Single-word and multi-word phrase search in O(k) trie time, then occurrence iteration.
Word-prefix completion	@ trigger: collects all trie words sharing the typed prefix via DFS.
Bigram next-word prediction	* trigger: a second trie indexes consecutive word pairs (bigrams). The top-N most-frequent successors of the last typed word are offered as ranked suggestions.
Search highlighting	Matched characters are rendered in yellow using SetConsoleTextAttribute. Highlights clear on the next edit.
Partial rendering	Only the affected row (or rows, after a merge/split) is redrawn, not the full screen.
File I/O	Load and save plain-text files. New files are created automatically. Prompted save on exit.

Key bindings

Ctrl+S      Save
Ctrl+Z      Undo
Ctrl+Y      Redo
Ctrl+F      Search (type query, Enter to confirm)
Arrows      Move cursor
Backspace   Delete left / merge lines
Enter       New line
Escape      Exit (save prompt)
@           Word-completion suggestions
*           Next-word prediction suggestions
1–9         Accept suggestion

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Architecture

Document model — 2-D doubly-linked list

sentinel─► c─► o─► n─► s─► o─► l─► e
   │                               │
   ▼                               ▼
sentinel─► p─► a─► d

Every row begins with a sentinel node whose data is '\n'. Characters within a row are linked left↔right. Corresponding column positions across rows are linked up↔down. This makes vertical cursor movement, line merge, and line split all local pointer operations — no array shifting.

SearchTrie

root
 └─ c
     └─ o
         └─ n  ← isWordEnd, OccurrenceList → {row:0, docNode:*}
         └─ s
             └─ o
                 └─ l
                     └─ e  ← isWordEnd, OccurrenceList → {row:0, docNode:*}

Each TrieNode stores an OccurrenceList — a singly-linked list of (Node*, row) pairs pointing back into the 2-D grid. Search reaches the terminal node in O(k), then iterates occurrences. For phrase search it verifies subsequent words starting from each first-word occurrence.

BigramPredictor

A second N-Ary trie keyed on the context word. Each terminal node holds a FollowerList of (word, frequency) pairs. On every word-boundary edit the trie is rebuilt in one O(n) pass; topN() does a simple selection over the (small) follower list.

"the" → { "quick": 3, "big": 1, "lazy": 2 }
"quick" → { "brown": 2, "fox": 1 }

Pressing @ after typing the yields: quick, lazy, big.

Undo / Redo

UndoStack is a fixed-capacity (50) singly-linked list acting as a stack. Each record stores the OpType and the minimal information needed to reverse it:

OpType	Stored data	Undo action
OP_INSERT	char, row, col	navigate → delete
OP_DELETE	char, row, col	navigate → insert
OP_NEWLINE	row, col	navigate to new row → merge
OP_MERGE	row, mergeCol	navigate → split

Rendering

The console is divided into three panels at startup. Only the panels that change are redrawn:

• displayRow(r) — redraws a single row after a character insert/delete.
• displayFrom(r) — redraws from row r downward after a line split/merge.
• display() — full repaint (used only on load and after undo of structural ops).

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File structure

ConsolePad/
│
├── include/
│   ├── Node.h              Core node type, UndoRecord, UndoStack declarations
│   ├── Notepad.h           Notepad class declaration
│   ├── SearchTrie.h        SearchTrie, MatchList, TrieNode declarations
│   ├── BigramPredictor.h   BigramPredictor, FollowerList declarations
│   └── UI.h                All rendering & panel function declarations
│
├── src/
│   ├── Main.cpp            Input loop and application orchestration
│   ├── Node.cpp            UndoStack implementation
│   ├── Notepad.cpp         Document editing, cursor, rendering, file I/O
│   ├── SearchTrie.cpp      Trie build, search, prefix completion
│   ├── BigramPredictor.cpp Bigram build and next-word suggestion
│   └── UI.cpp              Console primitives, panel rendering, highlights
│
├── screenshots/
└── README.md

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Screenshots

Main Menu

Search Panel

Suggestion System

Building

Requires: MSVC (Visual Studio 2019 or later) on Windows.

Visual Studio:

1. Create a new empty C++ project.
2. Add all files under src/ as source files and include/ as the include directory.
3. Build → Run.

Command line (MSVC):

cl /std:c++17 /W4 /I include src\*.cpp /Fe:ConsolePad.exe

The project uses <Windows.h> for console I/O (ReadConsoleInput, SetConsoleCursorPosition, SetConsoleTextAttribute). It is Windows-only by design.

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Known limitations

• Windows only. The rendering layer calls Win32 console APIs directly. Porting to POSIX would require replacing those calls with ncurses or equivalent.
• Full trie rebuild on each word boundary. Rebuilding is O(n) per word typed, which is acceptable for documents that fit on screen. An incremental update strategy (insert/remove individual words) would improve performance on very large files.
• No mouse support. Cursor movement is keyboard-only.
• Fixed 26-child trie alphabet. Non-ASCII characters in the source file are treated as word separators and are not indexed.

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Background

Built for CS218 Data Structures (Fall 2024). The bigram predictor was originally named ChilliMilliTree in the assignment spec — the name has been replaced with BigramPredictor for clarity, but the underlying structure is faithful to the original design.