Primitiivityypit: string, number, boolean

let username: string = 'Alice';
let score: number = 100;
let isLoggedIn: boolean = true;

let city = 'Istanbul';   // inferred as string
let price = 9.99;        // inferred as number
let enabled = false;     // inferred as boolean

let count: number = 10;
count = 'ten'; // Error: Type 'string' is not assignable to type 'number'

let greeting: string = 'Hello';
console.log(greeting.toUpperCase()); // 'HELLO'
console.log(greeting.length);        // 5

let age: number = 25;
let pi: number = 3.14159;
let hex: number = 0xFF;

let isDone: boolean = false;
let hasAccess: boolean = true;
// isDone = 1; // Error — not a boolean

let name: string = 'World';
let n: number = 42;
let msg = `Hello ${name}, you scored ${n}`;

// Correct
let a: string = 'hello';

// Avoid
let b: String = new String('hello'); // wrapper object

function add(a: number, b: number): number {
  return a + b;
}
add(2, 3);      // OK
// add(2, '3'); // Error

// Both are fine:
const x = 5;          // inferred number
const y: number = 5;  // explicit number