Because sometimes, you just want to think in boxes and arrows to be out of the box.
A visual flowchart interpreter built with C++17 and Qt 6, loosely following the spirit of Crafting Interpreters by Robert Nystrom except instead of typing code, you draw it.
demo.mp4
FlowPlusPlus lets you build programs visually, drag nodes onto a canvas, connect them with arrows, and hit Run. The interpreter walks the graph and executes your logic, node by node.
No syntax errors. No semicolons. Just flow (with the vibe).
| Shape | Flowchart Symbol | What it does |
|---|---|---|
| Rounded rectangle | Start / Stop | Marks the beginning and end of execution |
| Rectangle | Process | Assignment or expression — x = 5 + 3 |
| Diamond | Decision | Condition branches Yes (right) or No (bottom) |
| Parallelogram | Input / Output | Read from user or print a value |
- Visual canvas — dark-themed QGraphicsScene with pan, zoom, and fit-to-view
- Full interpreter — Lexer → Parser → AST → Graph Walker, built from scratch
- Variables — define and use variables across nodes (
x = 5,print x) - Control flow — loops and branches via Decision nodes and backward arrows
- Save / Load —
.fppJSON format, open and save your flowcharts - Undo / Redo — full history with Ctrl+Z / Ctrl+Y
- Copy / Paste — Ctrl+C / Ctrl+V with multi-select support
- Minimap — VSCode-style overview panel, click to pan
- Sample programs — 6 built-in examples via File → Open Sample
- Cross-platform — ships on Linux (Flatpak), Windows (.zip), and macOS (.dmg)
Node labels are mini-expressions evaluated at runtime:
# Process nodes
x = 10
result = x * 2 + 1
name = "Abby"
# Decision nodes (condition → Yes/No branch)
x > 5
remainder == 0
score >= 90
# Output nodes (auto-prefixed with print)
"Hello, World!"
"Result: " + result
x
# Input nodes (auto-prefixed with input)
x
score
Supported operators: + - * / % == != < <= > >= ! and or
Grab the latest release for your platform from the Releases page:
| Platform | File | Architecture | How to run |
|---|---|---|---|
| Linux | FlowPlusPlus-linux.flatpak |
x86_64 |
flatpak install FlowPlusPlus-linux.flatpak |
| Windows | FlowPlusPlus-windows-x64.zip |
x86_64 |
Extract and run FlowPlusPlus.exe |
| macOS | FlowPlusPlus-macos.dmg |
arm64 (Apple Silicon) |
Open DMG, drag to Applications |
git clone https://github.com/abhyuday-fr/FlowPlusPlus.git
cd FlowPlusPlus
cmake -B build -G Ninja -DCMAKE_BUILD_TYPE=Release
cmake --build build
./build/FlowPlusPlusRequirements: Qt 6.5+, CMake 3.19+, Ninja, C++17 compiler
Because FlowPlusPlus is not currently signed with an Apple Developer certificate, macOS Gatekeeper may flag it as "damaged" or "broken" when you first open the DMG or the App.
To fix this:
- Open your terminal.
- Run the following command to remove the quarantine flag:
# If you already moved it to Applications: xattr -cr /Applications/FlowPlusPlus.app # If you are still trying to open the DMG: xattr -cr FlowPlusPlus-macos.dmg
- Now you should be able to open the app normally.
Load any of these from File → Open Sample:
| Sample | What it shows |
|---|---|
| Hello World | Basic output node |
| Calculator | Input + arithmetic operations |
| Countdown | Loop with a Decision node |
| Even or Odd | Yes/No branching |
| Fibonacci | Complex loop with multiple variables |
| Grade Checker | Nested decision chains |
Node label (text)
↓
Lexer → tokens
↓
Parser → AST (Expr tree)
↓
evaluate() → Value (number / string / bool / nil)
↓
Graph walker → follows connections to next node
The flowchart is the program. Control flow comes from arrows, not keywords. Loops are just backward connections. Branches are Decision nodes.
See interpreter_explained_FPP.md for a deep dive.
Built chapter by chapter, following Crafting Interpreters:
- ✅ Chapter 1 — Canvas window, toolbar, dark theme
- ✅ Chapter 2 — FlowNode base class, FlowConnection
- ✅ Chapter 3 — Concrete node shapes (Start, Stop, Process, Decision, I/O)
- ✅ Chapter 4 — Placing nodes on canvas from toolbar
- ✅ Chapter 5 — Connecting nodes with arrows, Yes/No ports
- ✅ Chapter 6 — Value & Environment (variables, scope chain)
- ✅ Chapter 7 — Interpreter: Lexer, Parser, AST, Graph Walker
- ✅ Chapter 8 — Control flow, loops, error highlighting
- ✅ Chapter 9 — Save/Load (.fpp JSON format)
- ✅ Chapter 10 — Minimap
- ✅ Chapter 11 — Multi-select + Ctrl+C/Ctrl+V
- ✅ Chapter 12 — Undo/Redo (QUndoStack)
- ✅ Chapter 13 — Sample .fpp files
- ✅ Chapter 14 — Packaging + GitHub Actions CI/CD
can't wait to make a releasable version :)
I did it :D — it is live
The interpreter works. The canvas is solid. Here's what's on the roadmap:
Polish
- Autosave — periodic save to a temp file, recovery on crash
- "Unsaved changes" prompt on close / new file
- Grid snapping for cleaner node alignment
Power
- Export flowchart as PNG or SVG image
- Better interpreter error messages (highlight the failing node)
- System clipboard — copy/paste between separate FlowPlusPlus windows
Advanced
- Multiple Start nodes — run independent flowcharts sequentially
- Function subgraphs — call one flowchart from another
- Parallel execution via QThread
- C++17
- Qt 6.5+ — Widgets, QGraphicsScene, QUndoStack
- CMake + Ninja
- Flatpak (Linux distribution)
- GitHub Actions (CI/CD for Linux, Windows, macOS)
- Developed on Fedora Linux with Qt Creator
Issues and PRs are welcome. If you find a bug or want to add a node type, go for it.
MIT see license for details.
Built with way too much fun and not enough sleep.