C# for Beginners. Lessons 1: VARIABLES part 3
- Pavel Zosim
- Dec 6, 2025
- 3 min read
Updated: Dec 7, 2025
decimal ★ Money & Financial Calculations ★
Beginner explanation: The MOST precise decimal type, designed specifically for money and financial calculations. Has ~28-29 digits of precision and avoids the rounding errors that plague float/double. ALWAYS use decimal for currency, prices, and financial data. Much slower than float/double, so NEVER use in game loops or real-time calculations. Requires 'm' or 'M' suffix!
📊 Technical Specs:
Size: 16 bytes (128 bits)
Precision: ~28-29 significant digits
Range: ±1.0 × 10⁻²⁸ to ±7.9228 × 10²⁸
Default Value: 0.0m
⚡ Performance Notes:
❌ VERY SLOW - 10-100x slower than float/double
❌ No hardware acceleration (software-emulated)
❌ Uses 4x memory of float (16 vs 4 bytes)
✅ EXACT - no rounding errors for decimal values
✅ Perfect for financial calculations
💡 NEVER use in Update()/FixedUpdate() - too slow!
💡 Use ONLY for money, prices, currency
When to use decimal:
✅ Money/Currency (prices, costs, balances)
✅ Financial calculations (interest, tax, exchange rates)
✅ Accounting/billing systems
✅ Shop UI (display prices)
✅ Any calculation where exact decimal precision is legally required
❌ NEVER in game loops (Update, FixedUpdate)
❌ NEVER for positions, physics, transforms
❌ NEVER for real-time calculations
❌ Don't use if float/double are sufficient
💻 Syntax & Declaration:
🎮 Practical Use Cases:
⚠️ Common Pitfalls:
💡 Pro Tips:
char - Single Character
Beginner explanation: Stores a single character like 'A', '5', '@', or '中'. Uses single quotes, not double quotes! Internally it's just a number (0-65535) representing a Unicode character. Perfect for keyboard input, single letters, or text parsing.
📊 Technical Specs:
Size: 2 bytes (16 bits)
Range: '\u0000' to '\uffff' (0 to 65,535 - Unicode characters)
Default Value: '\0' (null character)
⚡ Performance Notes:
✅ Fast (just a 16-bit integer internally)
✅ 2 bytes (same as ushort)
✅ Good for menu systems, keyboard input
💡 String is usually more practical for text
💡 Use char for single-character operations only
When to use char:
✅ Single character storage
✅ Keyboard input (single key)
✅ Menu options (A, B, C, D)
✅ Character-by-character text parsing
✅ Grades, ratings (A, B, C)
✅ Direction indicators (N, S, E, W)
❌ Don't use for multi-character text (use string)
❌ Emojis need string (surrogate pairs)
💻 Syntax & Declaration:
🎮 Practical Use Cases:
⚠️ Common Pitfalls:
💡 Pro Tips:
string - Text Sequences
Beginner explanation: Stores text of any length - from empty "" to entire novels! Uses double quotes. Strings are IMMUTABLE (can't be changed after creation) - modifying a string actually creates a new one in memory. Use for names, messages, UI text, file paths - anything textual.
📊 Technical Specs:
Size: Dynamic (depends on text length)
Type: Reference type (stored on heap, not stack)
Immutable: Once created, cannot be modified
Default Value: null
⚡ Performance Notes:
⚠️ Immutable - every modification creates new string object
❌ Concatenation in loops is VERY slow (use StringBuilder)
✅ String interpolation ($"") is optimized by compiler
✅ String comparison is fast (interned strings)
💡 Use StringBuilder for 10+ concatenations
💡 Memory: Stores on heap (garbage collected)
When to use string:
✅ Player names, item names, descriptions
✅ UI text, dialogue, messages
✅ File paths, URLs
✅ JSON, XML, serialized data
✅ User input, commands
❌ Don't concatenate in loops (use StringBuilder)
❌ Don't use for single characters (use char)
💻 Syntax & Declaration:
🎮 Practical Use Cases:
⚠️ Common Pitfalls:
💡 Pro Tips:
bool - True/False Values
Beginner explanation: Stores only two values: true or false. Essential for game logic, conditions, and states. Think of it as an on/off switch, yes/no answer, or enabled/disabled flag. Uses 1 byte of memory despite being just 1 bit of information.
📊 Technical Specs:
Size: 1 byte (8 bits) - but logically 1 bit
Values: true or false only
Default Value: false
⚡ Performance Notes:
✅ Very fast (1 byte, simple operations)
✅ Comparison operators are optimized
✅ Short-circuit evaluation saves CPU
💡 Despite being 1 bit logically, uses 1 byte (memory alignment)
💡 For thousands of flags, consider bit packing
When to use bool:
✅ Any yes/no, true/false, on/off state
✅ Conditions and flags
✅ Ability checks (canJump, canAttack)
✅ State tracking (isAlive, isPaused)
✅ UI visibility (showMenu, isEnabled)
❌ Don't use int (0/1) instead of bool
❌ Don't use for multi-state (use enum instead)
💻 Syntax & Declaration:
🎮 Practical Use Cases:
⚠️ Common Pitfalls:
💡 Pro Tips:
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