// Control flow determines execution order
let hour = 14; // 2 PM
if (hour < 12) {
  console.log("Good morning!");
} else {
  console.log("Good afternoon!");
}

Good afternoon!

let temperature = 28;
if (temperature > 30) {
  console.log("It's hot!");
} else if (temperature > 20) {
  console.log("Nice weather!");
} else if (temperature > 10) {
  console.log("A bit chilly");
} else {
  console.log("Too cold!");
}

Nice weather!

let age = 25;
let hasLicense = true;

// AND operator (both must be true)
if (age >= 18 && hasLicense) {
  console.log("You can drive!");
}

// OR operator (at least one true)
if (age < 3 || age > 70) {
  console.log("Special ticket price applies");
}

// NOT operator
if (!hasLicense) {
  console.log("Cannot drive");
}

You can drive!

// Shorthand for simple if/else
let isMember = true;
let fee = isMember ? "$5.00" : "$10.00";
console.log(fee);

// Can be used for assignment or execution
let score = 85;
score > 90 ? console.log("Excellent!") : console.log("Good job!");

$5.00
Good job!

let day = "Tuesday";
let message;

switch (day) {
  case "Monday":
  case "Tuesday":
  case "Wednesday":
  case "Thursday":
    message = "Weekday";
    break;
  case "Friday":
    message = "Almost weekend!";
    break;
  case "Saturday":
  case "Sunday":
    message = "Weekend!";
    break;
  default:
    message = "Invalid day";
}
console.log(message);

Weekday

// Falsy values (evaluate to false):
false, 0, "", null, undefined, NaN

// Truthy values (evaluate to true):
true, 1, "hello", [], {}, 42, "0"

// Practical example:
let username = "";
if (username) {
  console.log("Welcome " + username);
} else {
  console.log("Please enter a username");
}

Please enter a username

// 1. Using assignment (=) instead of comparison (== or ===)
let loggedIn = false;
if (loggedIn = true) { /* ❌ Always true! */ }

// 2. Forgetting break in switch statements
case "Monday":
  message = "Start of week";
  // ❌ Missing break - will execute next case!

// 3. Confusing == and ===
if (0 == "0") { /* true */ }
if (0 === "0") { /* false */ }

// 4. Unnecessary else after return
if (x > 10) {
  return true;
} else {  // ❌ Unnecessary
  return false;
}

function assignGrade(score) {
  if (score >= 90) return "A";
  else if (score >= 80) return "B";
  else if (score >= 70) return "C";
  else if (score >= 60) return "D";
  else return "F";
}

// With switch (range example)
function getGradeComment(grade) {
  switch (grade) {
    case "A": return "Excellent!";
    case "B": return "Good job!";
    case "C": return "Average";
    case "D": return "Needs improvement";
    case "F": return "Failed";
    default: return "Invalid grade";
  }
}

assignGrade(85) → "B"
getGradeComment("B") → "Good job!"

// Grade button handler
document.getElementById("gradeBtn").addEventListener("click", () => {
  let score = parseInt(document.getElementById("scoreInput").value);
  let grade;

  if (score >= 90) grade = "A";
  else if (score >= 80) grade = "B";
  else if (score >= 70) grade = "C";
  else if (score >= 60) grade = "D";
  else grade = "F";

  document.getElementById("output").textContent = `Grade: ${grade}`;
});

// Weekday button handler
document.getElementById("weekdayBtn").addEventListener("click", () => {
  let day = document.getElementById("dayInput").value;
  let type;

  switch(day.toLowerCase()) {
    case "saturday":
    case "sunday":
      type = "weekend";
      break;
    case "monday":
    case "tuesday":
    case "wednesday":
    case "thursday":
    case "friday":
      type = "weekday";
      break;
    default:
      type = "invalid day";
  }

  document.getElementById("output").textContent = `Day type: ${type}`;
});