Variables & The C# Type System

In Plain English

C# is a strongly typed language where every variable has a defined type. C# offers rich primitives for numbers (int, double, decimal), text (char, string), boolean logic (bool), and smart type inference using the var keyword.

The Mental Model

"Variables are like labeled storage containers. You have a rigid steel box for whole bricks (int), a glass beaker for liquids with decimals (double), a cash register drawer for financial currency (decimal), and an envelope for letters (string)."

Deep Dive: How It Works

int: 32-bit whole integer (e.g. 42, -500).

double: 64-bit floating-point number (e.g. 3.14159). Fast, great for graphics and scientific math.

decimal: 128-bit ultra-precise decimal (e.g. 19.99m). Mandatory for financial and currency calculations to prevent floating-point rounding errors! (Requires "m" suffix).

bool: true or false.

char: Single Unicode character in single quotes (e.g. 'A', '#').

string: Sequence of characters in double quotes (e.g. "ZenCompiler").

var: Implicit typing—the compiler infers the exact type automatically from the assigned value (e.g. var speed = 100; becomes an int).

Syntax Blueprint

int score = 95;
double speed = 88.5;
decimal price = 14.99m;
bool isReady = true;
string name = "Neo";
var count = 10; // Inferred as int

Explicit typing (<type> <name> = <val>;) or implicit typing with var.

Core Rules to Remember

Strongly Typed: Variables cannot arbitrarily change type after being declared.

decimal for Money: Always use decimal with the 'm' suffix for money to avoid rounding glitches.

var is Still Statically Typed: var is not dynamic; the compiler locks in the type at compile time.

Common Beginner Traps & How to Fix Them

Mistake:Forgetting the 'm' suffix on decimal: decimal price = 9.99;

Why it happens: C# defaults decimal numbers to double without a suffix.

How to fix: Always write decimal price = 9.99m;.

Pro Tip: Use var when the variable type is obvious from the right side of the assignment (e.g. var list = new List<string>();)!

Live Interactive Example

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Declaring and Outputting C# Types

C# 12 / .NET

Output Console

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How it works: C# automatically formats numbers, booleans, and decimals when concatenated with strings.

Your Turn: Micro Challenge

No pressure! Edit the starter code below and test your solution with instant feedback.

Micro Exercise

Declare player variables

Declare string playerName = "Valkyrie";
Declare int health = 100;
Print "Player Valkyrie has 100 HP" by concatenating these variables.

Sandbox Output

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