Control Flow

Control flow statements allow you to control the execution path of your program based on conditions and loops.

Conditional Statements

If Statements

The basic if statement executes code when a condition is true:

fun main():
    age = 18

    if (age >= 18) then:
        print("You are an adult")
    end
end

If-Else Statements

Use else to provide an alternative when the condition is false:

fun main():
    temperature = 25

    if (temperature > 30) then:
        print("It's hot outside")
    else:
        print("It's not too hot")
    end
end

If-Else If-Else Chain

Chain multiple conditions using else if:

fun main():
    score = 85

    if (score >= 90) then:
        print("Grade: A")
    else if (score >= 80) then:
        print("Grade: B")
    else if (score >= 70) then:
        print("Grade: C")
    else if (score >= 60) then:
        print("Grade: D")
    else:
        print("Grade: F")
    end
end

Nested Conditions

fun main():
    age = 25
    has_license = true

    if (age >= 18) then:
        if (has_license) then:
            print("You can drive")
        else:
            print("You need a license to drive")
        end
    else:
        print("You are too young to drive")
    end
end

Ternary Operator

The ternary operator provides a concise way to write conditional expressions. It follows the format: condition ? true_value : false_value.

Basic Ternary Usage

fun main():
    age = 20
    status = age >= 18 ? "adult" : "minor"
    print("Status: " + status)  // Output: Status: adult
end

Nested Ternary Operators

You can chain ternary operators for multiple conditions:

fun classify_number(n):
    // Determine sign using nested ternary
    sign = n > 0 ? "positive" : n < 0 ? "negative" : "zero"

    // Determine parity
    parity = n % 2 == 0 ? "even" : "odd"

    return {
        "number": n,
        "sign": sign,
        "parity": parity,
        "absolute": n >= 0 ? n : -n
    }
end

fun main():
    result = classify_number(-5)
    print("Number: " + str(result["number"]))     // Number: -5
    print("Sign: " + result["sign"])             // Sign: negative
    print("Parity: " + result["parity"])         // Parity: odd
    print("Absolute: " + str(result["absolute"])) // Absolute: 5
end

Ternary in Function Returns

fun get_discount(age, is_student):
    // Calculate discount based on multiple conditions
    student_discount = is_student ? 0.1 : 0.0
    age_discount = age >= 65 ? 0.15 : age <= 12 ? 0.2 : 0.0

    // Return the maximum discount
    return student_discount > age_discount ? student_discount : age_discount
end

fun main():
    discount1 = get_discount(25, true)   // 0.1 (student discount)
    discount2 = get_discount(70, false)  // 0.15 (senior discount)
    discount3 = get_discount(8, false)   // 0.2 (child discount)

    print("Student discount: " + str(discount1 * 100) + "%")
    print("Senior discount: " + str(discount2 * 100) + "%")
    print("Child discount: " + str(discount3 * 100) + "%")
end

Ternary with String Formatting

fun format_time(hours, minutes, use_24h):
    // Convert to 12-hour format if needed
    formatted_hours = use_24h ? hours :
                      hours == 0 ? 12 :
                      hours > 12 ? hours - 12 : hours

    // Add AM/PM for 12-hour format
    period = use_24h ? "" : hours >= 12 ? " PM" : " AM"

    // Ensure two-digit formatting
    h_str = formatted_hours < 10 ? "0" + str(formatted_hours) : str(formatted_hours)
    m_str = minutes < 10 ? "0" + str(minutes) : str(minutes)

    return h_str +":" + m_str + period
end

fun main():
    print(format_time(9, 30, true))   // 09:30
    print(format_time(9, 30, false))  // 09:30 AM
    print(format_time(15, 45, false)) // 03:45 PM
    print(format_time(0, 15, false))  // 12:15 AM
end

Ternary in Array Operations

fun main():
    scores = [85, 92, 78, 96, 88]

    // Assign grades using ternary
    grades = []
    for (score in scores):
        grade = score >= 90 ? "A" : score >= 80 ? "B" : score >= 70 ? "C" : "F"
        append(grades, grade)
    end

    print("Scores: " + str(scores))
    print("Grades: " + str(grades))

    // Pass/fail results
    results = []
    for (score in scores):
        result = score >= 70 ? "PASS" : "FAIL"
        append(results, result)
    end

    print("Results: " + str(results))
end

Mathematical Expressions with Ternary

fun main():
    x = 10
    y = 7

    print("x = " + str(x) + ", y = " + str(y))
    print("max(x, y) = " + str(x > y ? x : y))           // 10
    print("min(x, y) = " + str(x < y ? x : y))           // 7
    print("|x - y| = " + str(x > y ? x - y : y - x))     // 3
    print("sign(x - y) = " + str(x > y ? 1 : x < y ? -1 : 0)) // 1
end

Complex Ternary Expressions

fun calculate_shipping(weight, is_priority, distance):
    // Calculate base rate based on weight
    base_rate = weight <= 1 ? 5.0 : weight <= 5 ? 8.0 : 12.0

    // Apply priority and distance multipliers
    priority_multiplier = is_priority ? 1.5 : 1.0
    distance_rate = distance > 1000 ? 1.2 : distance > 500 ? 1.1 : 1.0

    total = base_rate * priority_multiplier * distance_rate

    return {
        "cost": round(total, 2),
        "delivery_time": is_priority ?
                        distance > 1000 ? "2-3 days" : "1-2 days" :
                        distance > 1000 ? "5-7 days" : "3-5 days"
    }
end

fun main():
    shipping1 = calculate_shipping(0.5, false, 200)  // Light, standard, short
    shipping2 = calculate_shipping(8.0, true, 1500)  // Heavy, priority, long

    print("Standard shipping: $" + str(shipping1["cost"]) + " (" + shipping1["delivery_time"] + ")")
    print("Priority shipping: $" + str(shipping2["cost"]) + " (" + shipping2["delivery_time"] + ")")
end

When to Use Ternary vs If-Else

Use ternary when:

• You need a simple conditional assignment
• The expression is short and readable
• You're working with simple true/false conditions

// Good use of ternary
status = age >= 18 ? "adult" : "minor"
message = is_logged_in ? "Welcome back!" : "Please log in"
max_value = a > b ? a : b

Use if-else when:

• You have complex logic or multiple statements
• The condition involves multiple operations
• Readability would be compromised

// Better as if-else
if (user_score >= passing_grade) then:
    print("Congratulations! You passed!")
    update_user_status("passed")
    send_certificate(user)
else:
    print("Sorry, you didn't pass this time.")
    schedule_retake(user)
    send_study_materials(user)
end

Best Practices for Ternary Operators

1. Keep it simple: Don't nest too many ternary operators
2. Use parentheses: For clarity in complex expressions
3. Consider readability: If it's hard to read, use if-else instead
4. Format properly: Break long ternary expressions across lines

// Good: Simple and clear
result = condition ? value1 : value2

// Good: Properly formatted nested ternary
grade = score >= 90 ? "A" :
        score >= 80 ? "B" :
        score >= 70 ? "C" : "F"

// Avoid: Too complex
result = (a > b && c < d) ? (x > y ? complex_calc1(a, b) : complex_calc2(c, d)) : (z > w ? another_calc(x) : default_value)

Loops

While Loops

Execute code repeatedly while a condition is true:

fun main():
    count = 1

    while (count <= 5):
        print("Count: " + str(count))
        count = count + 1
    end

    print("Loop finished")
end

For Loops with Arrays

Iterate through arrays using for loops:

fun main():
    numbers = [1, 2, 3, 4, 5]

    for (num in numbers):
        print("Number: " + str(num))
    end
end

For Loops with Range

fun main():
    // Print numbers 1 to 10
    i = 1
    while (i <= 10):
        print("Number: " + str(i))
        i = i + 1
    end
end

Loop Control

Break Statement

Exit a loop early:

fun main():
    count = 1

    while (count <= 10):
        if (count == 5) then:
            print("Breaking at 5")
            break
        end

        print("Count: " + str(count))
        count = count + 1
    end
end

Continue Statement

Skip the current iteration:

fun main():
    count = 0

    while (count < 10):
        count = count + 1

        if (count % 2 == 0) then:
            continue  // Skip even numbers
        end

        print("Odd number: " + str(count))
    end
end

Practical Examples

Example 1: Number Guessing Game

fun main():
    secret_number = 7
    guess = 0
    attempts = 0
    max_attempts = 3

    print("Guess the number between 1 and 10!")

    while (attempts < max_attempts):
        // In a real program, you would get input from user
        // For demo, we'll simulate guesses
        if (attempts == 0) then:
            guess = 5
        else if (attempts == 1) then:
            guess = 8
        else:
            guess = 7
        end

        attempts = attempts + 1
        print("Attempt " + str(attempts) + ": Guessing " + str(guess))

        if (guess == secret_number) then:
            print("Congratulations! You guessed it!")
            break
        else if (guess < secret_number) then:
            print("Too low!")
        else:
            print("Too high!")
        end
    end

    if (guess != secret_number) then:
        print("Sorry, you ran out of attempts. The number was " + str(secret_number))
    end
end

Example 2: Array Processing

fun main():
    numbers = [12, 5, 8, 3, 16, 9, 1, 14]

    // Find maximum number
    max_num = numbers[0]
    for (num in numbers):
        if (num > max_num) then:
            max_num = num
        end
    end
    print("Maximum number: " + str(max_num))

    // Count even numbers
    even_count = 0
    for (num in numbers):
        if (num % 2 == 0) then:
            even_count = even_count + 1
        end
    end
    print("Even numbers count: " + str(even_count))

    // Sum of all numbers
    total = 0
    for (num in numbers):
        total = total + num
    end
    print("Sum of all numbers: " + str(total))
end

Example 3: Menu System

fun main():
    running = true
    choice = 1  // Simulate user choices

    while (running):
        print("\n=== Menu ===")
        print("1. Say Hello")
        print("2. Calculate Square")
        print("3. Exit")
        print("Choice: " + str(choice))

        if (choice == 1) then:
            print("Hello, World!")
            choice = 2  // Simulate next choice
        else if (choice == 2) then:
            number = 5
            square = number * number
            print("Square of " + str(number) + " is " + str(square))
            choice = 3  // Simulate next choice
        else if (choice == 3) then:
            print("Goodbye!")
            running = false
        else:
            print("Invalid choice")
            choice = 3  // Force exit
        end
    end
end

Best Practices

1. Keep Conditions Simple

// Good: Simple, readable condition
if (age >= 18 and has_license) then:
    print("Can drive")
end

// Avoid: Complex nested conditions
if (age >= 18) then:
    if (has_license) then:
        if (has_car) then:
            if (has_insurance) then:
                print("Can drive")
            end
        end
    end
end

2. Use Meaningful Variable Names

// Good: Descriptive names
is_valid_user = (age >= 18 and has_account)
if (is_valid_user) then:
    print("Access granted")
end

// Avoid: Unclear names
x = (a >= 18 and b)
if (x) then:
    print("Access granted")
end

3. Avoid Infinite Loops

// Good: Clear exit condition
count = 0
while (count < 10):
    print(count)
    count = count + 1  // Don't forget to update!
end

// Dangerous: Potential infinite loop
count = 0
while (count < 10):
    print(count)
    // Missing: count = count + 1
end

4. Use Early Returns When Appropriate

fun check_access(age, has_license):
    if (age < 18) then:
        return "Too young"
    end

    if (!has_license) then:
        return "No license"
    end

    return "Access granted"
end

Practice Exercises

Exercise 1: FizzBuzz

Write a program that prints numbers 1 to 20, but:

• Print "Fizz" for multiples of 3
• Print "Buzz" for multiples of 5
• Print "FizzBuzz" for multiples of both 3 and 5

Exercise 2: Prime Number Checker

Create a function that checks if a number is prime:

fun is_prime(n):
    // Your implementation here
    // Return true if n is prime, false otherwise
end

fun main():
    number = 17
    if (is_prime(number)) then:
        print(str(number) + " is prime")
    else:
        print(str(number) + " is not prime")
    end
end

Exercise 3: Array Search

Implement a linear search function:

fun find_element(array, target):
    // Your implementation here
    // Return the index if found, -1 if not found
end

fun main():
    numbers = [10, 25, 3, 8, 15]
    target = 8
    index = find_element(numbers, target)

    if (index != -1) then:
        print("Found " + str(target) + " at index " + str(index))
    else:
        print(str(target) + " not found")
    end
end

Summary

Control flow statements are essential for creating dynamic programs:

• Conditional statements (if, else) make decisions
• Loops (while, for) repeat operations
• Loop control (break, continue) provides fine-grained control
• Best practices ensure readable and maintainable code

Mastering control flow allows you to build complex logic and create interactive programs.

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Next: Learn about Functions to organize and reuse your code effectively.