🔧 Troubleshooting Guide

"command not found" or "is not recognized"

What it means: Your terminal can't find the program you're trying to run. The program either isn't installed, or it's not on your system PATH.

What to check:

• Did you install the software? Go back to Lesson 1.2 and run through the steps.
• Did you restart your terminal after installing? Many installers modify the PATH, but existing terminal sessions don't see the change.
• On Windows, did you check "Add to PATH" during installation? If not, uninstall and reinstall with that option selected.

How to check your PATH

# In PowerShell or Command Prompt:
echo %PATH%

# Or in PowerShell:
$env:PATH -split ";"

// In Terminal:
// echo $PATH
// Or see it split by colons:
// echo $PATH | tr ':' '\n'

// In Terminal:
// echo $PATH
// Or see it split by colons:
// echo $PATH | tr ':' '\n'

"Permission denied" errors

What it means: Your user account doesn't have permission to read, write, or execute a file or folder.

Fixes:

• Windows: Run your terminal as Administrator (right-click → "Run as administrator").
• macOS / Linux: Prefix the command with sudo (e.g., sudo npm install -g ...). Use sparingly — only for global installs.
• Make sure you're working inside a folder you own, like your home directory or Desktop, not a system folder.

Wrong version installed

What it means: You have an older version of a tool that doesn't support features used in this course.

How to check versions:

# Need 3.10 or higher
python --version
# or on some systems:
python3 --version

// Need Node.js 18 or higher
// node --version
// npm --version

// Need .NET SDK 8 or higher
// dotnet --version
// dotnet --list-sdks

Fix: Download and install the latest version from the official site. The new install will usually replace the old one automatically.

Multiple versions conflicting

Symptoms: Commands run a different version than expected, or libraries installed for one version aren't available in another.

Common scenario: You have both python (pointing to Python 2) and python3 (pointing to Python 3) on your system.

Fixes:

• Always use python3 and pip3 on macOS/Linux to be explicit.
• On Windows, use the Python Launcher: py -3 script.py.
• For Node.js, consider using nvm (Node Version Manager) to switch between versions.
• For .NET, use dotnet --list-sdks to see all installed versions, and set the version in a global.json file if needed.

"python" opens the Microsoft Store (Windows)

What's happening: Windows 10/11 ships with a stub python.exe that redirects to the Microsoft Store instead of running Python.

Fix:

• Open Settings → Apps → Advanced app settings → App execution aliases.
• Turn off the two entries for python.exe and python3.exe.
• Make sure Python is installed from python.org with "Add to PATH" checked.

"ModuleNotFoundError: No module named ..."

What it means: Python can't find a library you're trying to import.

Fixes:

• Install the module: pip install module_name (or pip3 install module_name).
• Make sure you're using the same Python that pip is linked to: python -m pip install module_name.
• If you're inside a virtual environment, make sure it's activated.

IndentationError / TabError

What it means: Python uses indentation to define code blocks, and your spacing is inconsistent.

Fixes:

• In VS Code, set "Insert Spaces" to true and "Tab Size" to 4 (the Python standard).
• Turn on "Render Whitespace" in VS Code to see spaces vs. tabs.
• Never mix tabs and spaces in the same file.

SyntaxError: invalid syntax (unexpected token)

Common causes:

• Missing colon at the end of if, for, while, def, or class lines.
• Using curly braces { } instead of indentation (mixing up with JS or C#).
• Using && or || instead of Python's and / or.
• Forgetting parentheses around print() (Python 2 habit).

"ReferenceError: require is not defined" (ES Modules)

What's happening: You're using import/export syntax (ES Modules) but Node.js defaults to CommonJS (require).

Fix: Add "type": "module" to your package.json, or name your file with a .mjs extension.

"SyntaxError: Cannot use import statement outside a module"

Same root cause as above. Node.js doesn't recognize import without being told to use ES Modules.

Quick fix: Run with node --experimental-modules file.js on older Node versions, or add "type": "module" to package.json.

npm EACCES permission error (macOS/Linux)

What's happening: npm is trying to install global packages in a system-owned directory.

Fix (recommended): Change npm's default directory to a user-owned folder:

mkdir ~/.npm-global
npm config set prefix '~/.npm-global'
# Add to your shell profile (~/.bashrc or ~/.zshrc):
export PATH=~/.npm-global/bin:$PATH

Then restart your terminal.

"TypeError: fetch is not a function" (older Node.js)

What's happening: The built-in fetch API was added in Node.js 18. Older versions don't have it.

Fix: Upgrade to Node.js 18+ (recommended for this course), or install the node-fetch package as a workaround.

Unexpected token / missing semicolons

Common in this course: If you're switching between Python and JavaScript, you might forget semicolons (optional but recommended in JS) or accidentally use Python syntax like elif instead of else if.

Tip: Install the ESLint extension in VS Code — it will underline syntax issues in real time.

"dotnet: command not found"

Fix: Install the .NET SDK (not just the Runtime). After installing, restart your terminal. On Linux, you may need to add ~/.dotnet to your PATH manually.

Top-level statements vs. traditional Main method

What's happening: Starting with .NET 6, C# supports "top-level statements" — you can write code directly in Program.cs without a class and Main() method. This course uses that style.

If you see errors about missing Main:

• Make sure you're on .NET 6 or later (dotnet --version).
• Your project file (.csproj) should target net8.0 or higher.
• Only one file in the project can use top-level statements.

"CS0246: The type or namespace name could not be found"

What it means: You're referencing a type that C# doesn't know about — usually a missing using directive or NuGet package.

Fixes:

• Add the correct using statement at the top of your file (e.g., using System.Text.Json;).
• If it's a third-party library, install the NuGet package: dotnet add package PackageName.
• VS Code's C# Dev Kit can auto-suggest missing usings — look for the lightbulb icon.

"error NETSDK1045: The current .NET SDK does not support targeting"

What's happening: The project targets a newer .NET version than what you have installed.

Fix: Either install the required SDK version, or change the TargetFramework in your .csproj file to match your installed version.

Build succeeded but nothing happens

Common cause: You're running dotnet build instead of dotnet run. Build only compiles; run both compiles and executes.

Also check: Make sure you're in the correct project folder (the one containing the .csproj file).

Extensions not working or not suggesting completions

Fixes:

• Make sure you have the recommended extensions: Python (Microsoft), C# Dev Kit (Microsoft), and ESLint.
• Reload VS Code: press Ctrl+Shift+P → "Developer: Reload Window".
• For Python, make sure the correct interpreter is selected: Ctrl+Shift+P → "Python: Select Interpreter".

Terminal in VS Code uses wrong shell

Fix: Open Settings → search for "Terminal Default Profile" → set it to your preferred shell (PowerShell on Windows, bash or zsh on macOS/Linux).

File encoding issues (weird characters in output)

What's happening: Your file might be saved in a different encoding than expected.

Fix: Click the encoding indicator in VS Code's bottom-right status bar → "Reopen with Encoding" → choose UTF-8. Then "Save with Encoding" → UTF-8.