Syntax and types

string name = "Ada";
int age = 28;
double price = 29.99;
bool isFree = false;

Console.WriteLine($"{name} is {age} years old");

C# is statically typed like Java, but with type inference via var when the type is obvious from context:

var courses = new List<string>(); // inferred as List<string>
var count = 5;                      // inferred as int

var doesn't make C# dynamically typed -- the compiler still pins down a single concrete type at compile time, it's just inferred rather than written out. var x = GetCourse(); is exactly as strict as Course x = GetCourse();; the difference is purely how much you type. Use var when the right-hand side already makes the type obvious, and spell out the type explicitly when it wouldn't be (e.g. int result = ComputeScore(); when ComputeScore's return type isn't clear from the name).

C# distinguishes value types from reference types, which matters for how assignment behaves. int, double, bool, and structs are value types -- assigning one variable to another copies the value:

int a = 5;
int b = a; // b is an independent copy
b = 10;
Console.WriteLine(a); // still 5

string, arrays, and any class are reference types -- assignment copies the reference, so both variables point at the same underlying object:

var list1 = new List<int> { 1, 2, 3 };
var list2 = list1;   // same list, not a copy
list2.Add(4);
Console.WriteLine(list1.Count); // 4 -- list1 sees list2's change too

String is a special case worth calling out: it's a reference type, but it's immutable -- every operation that looks like it modifies a string (ToUpper(), Replace(...), Substring(...)) actually returns a brand-new string rather than changing the original. This is why str.ToUpper(); on its own line, without assigning the result somewhere, silently does nothing useful.