Variables

Variables in C#

A variable is a symbolic name given to a memory location. In C#, variables are categorized into two main types based on how they store data in memory: Value Types and Reference Types.

1. Value Types

Value types store the actual data directly in the location where the variable is declared (usually on the stack). When you copy a value type, a complete independent copy of the data is made.

int original = 100; int copy = original; 
// A new copy is created copy = 200; 
// Changing the copy does NOT affect the original 
Console.WriteLine("Original: {original}, Copy: {copy}"); 

2. Reference Types

Reference types do not store the actual data. Instead, they store a reference (a pointer) to the memory address where the data is kept (usually on the heap). When you copy a reference type, you are only copying the pointer, not the data itself.

int[] originalArray = { 1, 2, 3 }; int[] aliasArray = originalArray; 
// Both variables point to the same memory aliasArray[0] = 99; 
// Changing aliasArray affects originalArray 
Console.WriteLine("Original[0]: {originalArray[0]}, Alias[0]: {aliasArray[0]}");     

Variable Declaration and Initialization

C# is a strongly-typed language. You must declare the type of a variable before you use it. You can also use the var keyword for implicit typing, where the compiler determines the type based on the value assigned.

Examples

.. Admonition:: Example 1 : Explicit vs Implicit Typing

double precision = 0.0001; //Explicit
var tolerance = 1e-6; // Implicit (compiler sees it is a double) 
Console.WriteLine($"Precision: {precision}, Tolerance: {tolerance}");

Precision: 0.0001, Tolerance: 1E-06

.. Admonition:: Example 2 : Constant Variables

const double Gravity = 9.81; 
// Gravity = 10; 
// This would cause a compilation error 
Console.WriteLine($"Acceleration due to gravity: {Gravity} m/s²"); 

Acceleration due to gravity: 9.81 m/s²

.. Admonition:: Example 3 : Scope and Braces

int outer = 10; 
{ 
    int inner = 20; 
    Console.WriteLine($"Sum: {outer + inner}"); 
} 
// Console.WriteLine(inner); 
// Error: 'inner' is out of scope 

Sum: 30

.. Admonition:: Example 4 : Nullable Reference Types

string? name = null; 
// The '?' allows the reference to be null 
name = "Sepal Solver"; 
Console.WriteLine($"Project: {name}"); 

Project: Sepal Solver