Variables and Data Types

Storing Values in Variables

C++ is statically typed — you must declare the type of every variable:

int    age    = 25;        // whole numbers
double price  = 9.99;      // floating-point (preferred over float)
char   grade  = 'A';       // single character (single quotes!)
bool   active = true;      // true or false
string name   = "Alice";   // text (needs #include <string>)

const — values that never change

const double PI = 3.14159265;
const int MAX_USERS = 100;

auto — let the compiler infer the type

auto x = 42;       // int
auto y = 3.14;     // double

Your Task

Write circleArea(double radius) that returns the area of a circle.
Formula: area = PI * r * r — use 3.14159265 for PI.