Operators (Arithmetic, Comparison, Logical)

// In this expression:
5 + 3

// "+" is the operator
// "5" and "3" are the operands
// The result is 8

let x = 10;
// "=" is the assignment operator
// "x" is the left operand
// "10" is the right operand

// Addition (+)
console.log(10 + 5);   // 15
console.log(2.5 + 3.7); // 6.2

// Subtraction (-)
console.log(10 - 5);   // 5
console.log(3.7 - 2.5); // 1.2

// Multiplication (*)
console.log(10 * 5);   // 50
console.log(2.5 * 4);  // 10

// Division (/)
console.log(10 / 5);   // 2
console.log(10 / 3);   // 3.3333333333333335

// Modulus (%) - remainder after division
console.log(10 % 3);   // 1 (10 divided by 3 is 3 remainder 1)
console.log(15 % 4);   // 3 (15 divided by 4 is 3 remainder 3)
console.log(20 % 5);   // 0 (20 divided by 5 is 4 remainder 0)

// Exponentiation (**) - power
console.log(2 ** 3);   // 8 (2 to the power of 3)
console.log(5 ** 2);   // 25 (5 squared)
console.log(10 ** 0);  // 1 (anything to power 0 is 1)

// Check if number is even or odd
let num = 17;
if (num % 2 === 0) {
  console.log("Even");
} else {
  console.log("Odd");  // This executes
}

// Check if number is divisible by another
let score = 150;
if (score % 10 === 0) {
  console.log("Score is divisible by 10"); // Executes
}

// Cycle through values (wrapping)
let items = 5;
let currentIndex = 7;
let actualIndex = currentIndex % items;
console.log(actualIndex); // 2 (7 % 5 = 2)

// Get last digit of a number
let number = 12345;
let lastDigit = number % 10;
console.log(lastDigit); // 5

// JavaScript follows PEMDAS/BODMAS rules
// Parentheses/Brackets, Exponents, Multiplication/Division, Addition/Subtraction

console.log(2 + 3 * 4);      // 14 (not 20) - multiply first
console.log((2 + 3) * 4);    // 20 - parentheses first

console.log(10 - 2 + 3);     // 11 (left to right for same precedence)
console.log(10 / 2 * 3);     // 15 (left to right)

console.log(2 ** 3 ** 2);    // 512 (exponents are right to left!)
// This is 2 ** (3 ** 2) = 2 ** 9 = 512
// Not (2 ** 3) ** 2 = 8 ** 2 = 64

// Complex expression
let result = 10 + 2 * 5 - 3 ** 2;
console.log(result);         // 11
// Step 1: 3 ** 2 = 9
// Step 2: 2 * 5 = 10
// Step 3: 10 + 10 = 20
// Step 4: 20 - 9 = 11

// Simple assignment
let x = 10;
let name = "John";
let isActive = true;

// Chained assignment (not recommended for clarity)
let a, b, c;
a = b = c = 5;
console.log(a, b, c); // 5 5 5

let x = 10;

// Addition assignment (+=)
x += 5;  // Same as: x = x + 5
console.log(x);  // 15

// Subtraction assignment (-=)
x -= 3;  // Same as: x = x - 3
console.log(x);  // 12

// Multiplication assignment (*=)
x *= 2;  // Same as: x = x * 2
console.log(x);  // 24

// Division assignment (/=)
x /= 4;  // Same as: x = x / 4
console.log(x);  // 6

// Modulus assignment (%=)
x %= 4;  // Same as: x = x % 4
console.log(x);  // 2

// Exponentiation assignment (**=)
x **= 3;  // Same as: x = x ** 3
console.log(x);  // 8

// Increment score
let score = 0;
score += 10;  // Add 10 points
score += 5;   // Add 5 more points
console.log(score);  // 15

// Apply discount
let price = 100;
price *= 0.9;  // 10% discount (multiply by 0.9)
console.log(price);  // 90

// Accumulate totals
let total = 0;
total += 50;   // First purchase
total += 30;   // Second purchase
total += 20;   // Third purchase
console.log(total);  // 100

// Update inventory
let inventory = 100;
inventory -= 15;  // Sold 15 items
console.log(inventory);  // 85

let count = 0;

// Post-increment (use current value, then increment)
console.log(count++);  // 0 (uses 0, then increments)
console.log(count);    // 1

// Pre-increment (increment, then use new value)
count = 0;
console.log(++count);  // 1 (increments, then uses 1)
console.log(count);    // 1

// Practical example
let likes = 10;
likes++;  // Same as: likes = likes + 1
console.log(likes);  // 11

let count = 10;

// Post-decrement
console.log(count--);  // 10 (uses 10, then decrements)
console.log(count);    // 9

// Pre-decrement
count = 10;
console.log(--count);  // 9 (decrements, then uses 9)
console.log(count);    // 9

// Practical example
let itemsLeft = 5;
itemsLeft--;  // Same as: itemsLeft = itemsLeft - 1
console.log(itemsLeft);  // 4

// For standalone statements, both work the same
let x = 5;
x++;      // x is now 6
++x;      // x is now 7

// Difference matters in expressions
let a = 5;
let b = a++;  // b = 5, a = 6 (use then increment)

let c = 5;
let d = ++c;  // d = 6, c = 6 (increment then use)

// Most common: standalone increment/decrement
for (let i = 0; i < 5; i++) {  // i++ is clearest
  console.log(i);
}

// Strict equality (===) - checks value AND type
console.log(5 === 5);        // true
console.log(5 === "5");      // false (different types)
console.log(true === 1);     // false (different types)

// Strict inequality (!==) - opposite of ===
console.log(5 !== 5);        // false
console.log(5 !== "5");      // true (different types)
console.log(true !== 1);     // true (different types)

// Loose equality (==) - checks value only (with type coercion)
console.log(5 == "5");       // true (string "5" converted to number)
console.log(true == 1);      // true (true converted to 1)
console.log(false == 0);     // true (false converted to 0)
console.log("" == 0);        // true (empty string converted to 0)

// Loose inequality (!=) - opposite of ==
console.log(5 != "5");       // false
console.log(5 != 6);         // true

// Greater than (>)
console.log(10 > 5);         // true
console.log(5 > 10);         // false
console.log(5 > 5);          // false (not greater, equal)

// Less than (<)
console.log(5 < 10);         // true
console.log(10 < 5);         // false
console.log(5 < 5);          // false

// Greater than or equal (>=)
console.log(10 >= 5);        // true
console.log(5 >= 5);         // true
console.log(3 >= 5);         // false

// Less than or equal (<=)
console.log(5 <= 10);        // true
console.log(5 <= 5);         // true
console.log(10 <= 5);        // false

// String comparison (alphabetical)
console.log("a" < "b");      // true
console.log("apple" < "banana"); // true
console.log("Z" < "a");      // true (uppercase before lowercase)

// Age verification
let age = 18;
if (age >= 18) {
  console.log("Adult");
}

// Grade checking
let score = 85;
if (score >= 90) {
  console.log("A");
} else if (score >= 80) {
  console.log("B");  // This executes
}

// Price comparison
let budget = 1000;
let price = 850;
if (price <= budget) {
  console.log("Can afford");  // Executes
}

// String equality (case-sensitive!)
let input = "yes";
if (input === "yes") {
  console.log("Confirmed");
}

// Be careful with types
let userAge = "18";  // String from input
if (userAge === 18) {
  console.log("Adult");  // Won't execute! Different types
}
if (Number(userAge) === 18) {
  console.log("Adult");  // Executes - converted to number
}

// Basic AND
console.log(true && true);    // true
console.log(true && false);   // false
console.log(false && true);   // false
console.log(false && false);  // false

// Practical examples
let age = 25;
let hasLicense = true;

if (age >= 18 && hasLicense) {
  console.log("Can drive");  // Executes (both true)
}

// Multiple conditions
let score = 85;
let attendance = 95;
let homework = true;

if (score >= 80 && attendance >= 90 && homework) {
  console.log("Honor roll");  // Executes (all true)
}

// Range checking
let temperature = 72;
if (temperature >= 60 && temperature <= 80) {
  console.log("Comfortable");  // Executes
}

// Basic OR
console.log(true || true);    // true
console.log(true || false);   // true
console.log(false || true);   // true
console.log(false || false);  // false

// Practical examples
let isWeekend = true;
let isHoliday = false;

if (isWeekend || isHoliday) {
  console.log("Day off");  // Executes (one is true)
}

// Multiple options
let payment = "credit";
if (payment === "cash" || payment === "credit" || payment === "debit") {
  console.log("Payment accepted");  // Executes
}

// Default values
let username = "";
let displayName = username || "Guest";
console.log(displayName);  // "Guest" (username is falsy)

// Basic NOT
console.log(!true);           // false
console.log(!false);          // true

// Double NOT converts to boolean
console.log(!!"hello");       // true
console.log(!!0);             // false

// Practical examples
let isLoggedIn = false;
if (!isLoggedIn) {
  console.log("Please log in");  // Executes
}

// Checking for empty
let username = "";
if (!username) {
  console.log("Username required");  // Executes
}

// Inverting conditions
let hasErrors = true;
if (!hasErrors) {
  console.log("Form is valid");
} else {
  console.log("Fix errors");  // Executes
}

// AND has higher precedence than OR
let a = true;
let b = false;
let c = true;

console.log(a || b && c);  // true
// Same as: a || (b && c)
// (b && c) = false, then (a || false) = true

// Use parentheses for clarity
let age = 25;
let hasLicense = true;
let hasInsurance = false;
let hasCar = true;

// Can drive if: (18+ AND has license) AND (has insurance OR has car)
if ((age >= 18 && hasLicense) && (hasInsurance || hasCar)) {
  console.log("Can drive");  // Executes
}

// Complex example: discount eligibility
let isMember = true;
let cartTotal = 150;
let hasCode = false;

if (isMember && (cartTotal >= 100 || hasCode)) {
  console.log("Eligible for discount");  // Executes
}

// AND (&&) stops at first falsy value
console.log(false && expensive());  // false (expensive() never runs)
console.log(true && "value");       // "value" (returns second value)

// OR (||) stops at first truthy value
console.log(true || expensive());   // true (expensive() never runs)
console.log(false || "default");    // "default" (returns second value)

// Practical: default values
let userColor = "";
let color = userColor || "blue";
console.log(color);  // "blue"

// Practical: conditional execution
let isAdmin = true;
isAdmin && console.log("Admin access granted");  // Executes

// Practical: safe property access
let user = null;
let name = user && user.name;  // null (doesn't error)
console.log(name);  // null

// condition ? valueIfTrue : valueIfFalse

let age = 20;
let status = age >= 18 ? "Adult" : "Minor";
console.log(status);  // "Adult"

// Equivalent if-else
let status2;
if (age >= 18) {
  status2 = "Adult";
} else {
  status2 = "Minor";
}
console.log(status2);  // "Adult"

// Simple assignment
let score = 85;
let grade = score >= 60 ? "Pass" : "Fail";
console.log(grade);  // "Pass"

// In template literals
let temp = 30;
let message = `It's ${temp >= 25 ? "hot" : "cool"} today`;
console.log(message);  // "It's hot today"

// Function arguments
function greet(name) {
  console.log(`Hello, ${name || "Guest"}!`);
}
greet();         // "Hello, Guest!"
greet("John");   // "Hello, John!"

// Return values
function getDiscount(isMember) {
  return isMember ? 0.2 : 0.1;
}
console.log(getDiscount(true));   // 0.2
console.log(getDiscount(false));  // 0.1

// Conditional rendering (common in React)
let isLoggedIn = true;
let button = isLoggedIn ? "Logout" : "Login";
console.log(button);  // "Logout"

// Nested ternary for multiple conditions
let score = 85;
let grade = score >= 90 ? "A" :
            score >= 80 ? "B" :
            score >= 70 ? "C" :
            score >= 60 ? "D" : "F";
console.log(grade);  // "B"

// Better: use if-else for complex logic
let grade2;
if (score >= 90) {
  grade2 = "A";
} else if (score >= 80) {
  grade2 = "B";
} else if (score >= 70) {
  grade2 = "C";
} else if (score >= 60) {
  grade2 = "D";
} else {
  grade2 = "F";
}
console.log(grade2);  // "B" (more readable)

// Check types
console.log(typeof 42);          // "number"
console.log(typeof "hello");     // "string"
console.log(typeof true);        // "boolean"
console.log(typeof undefined);   // "undefined"
console.log(typeof null);        // "object" (JavaScript quirk!)
console.log(typeof {});          // "object"
console.log(typeof []);          // "object"
console.log(typeof function(){}); // "function"

// Practical use: validation
function process(value) {
  if (typeof value === "string") {
    console.log("Processing string:", value.toUpperCase());
  } else if (typeof value === "number") {
    console.log("Processing number:", value * 2);
  } else {
    console.log("Unknown type");
  }
}

process("hello");  // Processing string: HELLO
process(42);       // Processing number: 84

// Complex expression
let result = 5 + 3 * 2 > 10 && true;
console.log(result);  // true

// Step by step:
// 1. 3 * 2 = 6
// 2. 5 + 6 = 11
// 3. 11 > 10 = true
// 4. true && true = true

// Use parentheses to be clear
let result2 = ((5 + (3 * 2)) > 10) && true;
console.log(result2);  // true (same result, clearer intent)

function validateForm(username, password, age) {
  // Check if all fields are filled
  if (!username || !password || !age) {
    return "All fields are required";
  }
  
  // Username validation
  if (username.length < 3 || username.length > 20) {
    return "Username must be 3-20 characters";
  }
  
  // Password validation
  if (password.length < 8) {
    return "Password must be at least 8 characters";
  }
  
  // Age validation
  let ageNum = Number(age);
  if (isNaN(ageNum) || ageNum < 13 || ageNum > 120) {
    return "Invalid age";
  }
  
  return "Valid form!";
}

console.log(validateForm("john", "pass123456", "25"));
// "Valid form!"

function calculateTotal(price, quantity, isMember, hasCode) {
  // Base calculation
  let subtotal = price * quantity;
  
  // Member discount (10%)
  let memberDiscount = isMember ? subtotal * 0.1 : 0;
  
  // Promo code discount (additional 5%)
  let codeDiscount = hasCode ? subtotal * 0.05 : 0;
  
  // Total discounts
  let totalDiscount = memberDiscount + codeDiscount;
  
  // Apply discounts
  let total = subtotal - totalDiscount;
  
  // Free shipping if over $50
  let shipping = total >= 50 ? 0 : 5.99;
  
  // Final total
  let finalTotal = total + shipping;
  
  return {
    subtotal: subtotal.toFixed(2),
    discount: totalDiscount.toFixed(2),
    shipping: shipping.toFixed(2),
    total: finalTotal.toFixed(2)
  };
}

console.log(calculateTotal(25, 3, true, true));
// { subtotal: "75.00", discount: "11.25", shipping: "0.00", total: "63.75" }

function calculateGrade(scores) {
  // Calculate average
  let sum = 0;
  for (let i = 0; i < scores.length; i++) {
    sum += scores[i];
  }
  let average = sum / scores.length;
  
  // Determine letter grade
  let grade = average >= 90 ? "A" :
              average >= 80 ? "B" :
              average >= 70 ? "C" :
              average >= 60 ? "D" : "F";
  
  // Determine status
  let passed = average >= 60;
  let honors = average >= 90;
  
  return {
    average: average.toFixed(1),
    grade: grade,
    passed: passed,
    honors: honors
  };
}

console.log(calculateGrade([85, 92, 78, 95]));
// { average: "87.5", grade: "B", passed: true, honors: false }