Q11. What is the difference between function declaration and function expression?

// function declaration
function add(a, b) {
  return a + b;
}

// function expression
const multiply = function (a, b) {
  return a * b;
};

// নামসহ function expression (recursion ও debugging-এ কাজে লাগে)
const factorial = function fact(n) {
  return n <= 1 ? 1 : n * fact(n - 1);
};

sayHi(); // ✅ কাজ করে — উপরে উঠে গেছে
function sayHi() {
  console.log("Hi!");
}

// greet(); // ❌ ReferenceError
greet(); // এখন চলে
const greet = function () {
  console.log("Hello!");
};
greet();