🔀 Lesson 3.1: Conditionals — if, else, and switch

# Python: colon + indentation (no braces!)
temperature = 35

if temperature > 30:
    print("It's hot outside!")
    print("Stay hydrated!")

print("This always runs — it's outside the if block")

// JavaScript: parentheses around condition + curly braces
let temperature = 35;

if (temperature > 30) {
    console.log("It's hot outside!");
    console.log("Stay hydrated!");
}

console.log("This always runs — it's outside the if block");

// C#: same as JavaScript — parentheses + curly braces
int temperature = 35;

if (temperature > 30)
{
    Console.WriteLine("It's hot outside!");
    Console.WriteLine("Stay hydrated!");
}

Console.WriteLine("This always runs — it's outside the if block");

age = 16

if age >= 18:
    print("You can vote!")
else:
    print(f"You can vote in {18 - age} year(s).")

let age = 16;

if (age >= 18) {
    console.log("You can vote!");
} else {
    console.log(`You can vote in ${18 - age} year(s).`);
}

int age = 16;

if (age >= 18)
{
    Console.WriteLine("You can vote!");
}
else
{
    Console.WriteLine($"You can vote in {18 - age} year(s).");
}

score = 85

if score >= 90:
    grade = "A"
elif score >= 80:
    grade = "B"
elif score >= 70:
    grade = "C"
elif score >= 60:
    grade = "D"
else:
    grade = "F"

print(f"Score: {score} → Grade: {grade}")  # Score: 85 → Grade: B

let score = 85;
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";
}

console.log(`Score: ${score} → Grade: ${grade}`);

int score = 85;
string 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";
}

Console.WriteLine($"Score: {score} → Grade: {grade}");

# Python: indentation IS the code block
# The colon (:) starts the block
# Everything indented one level deeper belongs to the block

if True:
    print("Inside the if")     # ← indented: part of if
    print("Still inside")      # ← indented: part of if
print("Outside the if")        # ← not indented: NOT part of if

# WRONG — inconsistent indentation:
# if True:
#     print("line 1")
#   print("line 2")    # IndentationError!

# Use 4 spaces per level (Python convention)

// JavaScript: braces define the block
// Indentation is for readability only (not enforced)

if (true) {
    console.log("Inside the if");   // inside braces
    console.log("Still inside");    // inside braces
}
console.log("Outside the if");      // after closing brace

// This works but is UGLY (don't do this):
if (true) {
console.log("no indentation");
console.log("hard to read");
}

// Use 2 or 4 spaces per level (team preference)

// C#: braces define the block (same as JavaScript)
// C# convention: opening brace on its own line

if (true)
{
    Console.WriteLine("Inside the if");
    Console.WriteLine("Still inside");
}
Console.WriteLine("Outside the if");

// Alternate style (opening brace on same line):
// if (true) {
//     Console.WriteLine("Also valid");
// }
// Both styles work — be consistent within a project

# Python: == compares values, 'is' compares identity
print(5 == 5.0)        # True (same value)
print(5 is 5.0)        # False (different types/objects)
print("hello" == "hello")  # True

# Python also lets you chain comparisons!
age = 25
print(18 <= age <= 65)  # True — is age between 18 and 65?
# This is unique to Python and very readable

// JavaScript: === (strict) vs == (loose) — ALWAYS use ===
console.log(5 === 5);      // true
console.log(5 === "5");    // false (different types)
console.log(5 == "5");     // true! (loose: converts, then compares)
console.log(0 == false);   // true! (loose equality strikes again)
console.log(0 === false);  // false (strict: different types)

// Rule: ALWAYS use === and !== in JavaScript
// The only exception: checking for null/undefined
console.log(null == undefined);   // true
console.log(null === undefined);  // false

// C#: == works correctly (no loose equality issue)
Console.WriteLine(5 == 5);          // True
// Console.WriteLine(5 == "5");     // Compile error! Can't compare
Console.WriteLine("hello" == "hello");  // True

// String comparison is case-sensitive by default
Console.WriteLine("Hello" == "hello");  // False

// Case-insensitive comparison:
Console.WriteLine(string.Equals("Hello", "hello",
    StringComparison.OrdinalIgnoreCase));  // True

# Python 3.10+: match/case (structural pattern matching)
day = "Monday"

match day:
    case "Monday":
        print("Start of the work week")
    case "Friday":
        print("Almost weekend!")
    case "Saturday" | "Sunday":
        print("Weekend!")
    case _:
        print("Midweek day")

# The _ is the wildcard — matches anything (like 'default')
# The | means "or" — matches either pattern

# Before Python 3.10, use if/elif chains instead

// JavaScript: classic switch/case
let day = "Monday";

switch (day) {
    case "Monday":
        console.log("Start of the work week");
        break;
    case "Friday":
        console.log("Almost weekend!");
        break;
    case "Saturday":
    case "Sunday":
        console.log("Weekend!");
        break;
    default:
        console.log("Midweek day");
}

// WARNING: forgetting 'break' causes "fall-through"
// — execution continues into the next case!

// C#: switch with no fall-through (safer than JavaScript)
string day = "Monday";

switch (day)
{
    case "Monday":
        Console.WriteLine("Start of the work week");
        break;
    case "Friday":
        Console.WriteLine("Almost weekend!");
        break;
    case "Saturday":
    case "Sunday":
        Console.WriteLine("Weekend!");
        break;
    default:
        Console.WriteLine("Midweek day");
        break;
}

// C# switch expressions (modern, concise):
string message = day switch
{
    "Monday" => "Start of the work week",
    "Friday" => "Almost weekend!",
    "Saturday" or "Sunday" => "Weekend!",
    _ => "Midweek day"
};
Console.WriteLine(message);

# Python: value_if_true if condition else value_if_false
age = 20
status = "adult" if age >= 18 else "minor"
print(status)  # adult

# Works in f-strings too:
print(f"You are {'old enough' if age >= 21 else 'too young'} to drink.")

# Don't nest ternaries — they get unreadable fast
# bad = "A" if x > 90 else "B" if x > 80 else "C"  # confusing!

// JavaScript: condition ? value_if_true : value_if_false
let age = 20;
let status = age >= 18 ? "adult" : "minor";
console.log(status);  // adult

// Works in template literals too:
console.log(`You are ${age >= 21 ? "old enough" : "too young"} to drink.`);

// Don't nest ternaries:
// let bad = x > 90 ? "A" : x > 80 ? "B" : "C";  // hard to read

// C#: same as JavaScript — condition ? true : false
int age = 20;
string status = age >= 18 ? "adult" : "minor";
Console.WriteLine(status);  // adult

// Works in interpolation:
Console.WriteLine($"You are {(age >= 21 ? "old enough" : "too young")} to drink.");

// Note: C# requires parentheses around ternary in interpolation