chapter03.md

Chapter 3: Control Flow

Control flow statements are the backbone of any programming language, allowing you to execute different blocks of code based on conditions or to repeat actions multiple times. This chapter explores NAAb's constructs for managing program flow.

3.1 Conditional Execution: if, else if, and else

NAAb uses if, else if, and else statements to execute code conditionally. The condition inside an if or else if statement must evaluate to a boolean (true or false). Unlike some languages, parentheses around the condition are optional.

main {
    let temperature = 25

    // Basic if statement
    if temperature > 20 {
        print("It's a warm day!")
    }

    // if-else statement
    if temperature < 10 {
        print("It's cold!")
    } else {
        print("It's not too cold.")
    }

    // if-else if-else chain
    let score = 85
    if score >= 90 {
        print("Grade: A")
    } else if score >= 80 {
        print("Grade: B")
    } else if score >= 70 {
        print("Grade: C")
    } else {
        print("Grade: F")
    }
}

Output of the above code:

It's a warm day!
It's not too cold.
Grade: B

3.2 Loops: while and for..in

NAAb provides while loops for repeating a block of code as long as a condition is true, and for..in loops for iterating over collections.

3.2.1 The while Loop

A while loop continues to execute its body as long as its condition remains true. It's crucial to ensure the condition eventually becomes false to avoid infinite loops.

main {
    let countdown = 3
    print("Starting countdown...")
    while countdown > 0 {
        print(" ", countdown, "...")
        countdown = countdown - 1 // Decrement to eventually end the loop
    }
    print("Liftoff!")
}

Output of the above code:

Starting countdown...
 3 ...
 2 ...
 1 ...
Liftoff!

3.2.2 The for..in Loop

The for..in loop is used to iterate over elements of collections like arrays. It assigns each element, in turn, to a specified variable for the duration of one loop iteration.

main {
    let fruits = ["apple", "banana", "cherry"]
    print("Available fruits:")
    for fruit in fruits {
        print(" - ", fruit)
    }

    let user_data = {"name": "Alice", "age": 30, "city": "New York"}
    print("User data details:")
    for key in user_data { // Iterating over keys of a dictionary
        print(" - ", key, ": ", user_data[key])
    }
}

Output of the above code:

Available fruits:
 -  apple
 -  banana
 -  cherry
User data details:
 -  name : Alice
 -  age : 30
 -  city : New York

3.2.3 Range Loops

NAAb supports numeric ranges for iterating a specific number of times.

• Exclusive Range (..): Iterates from start up to (but not including) end.
• Inclusive Range (..=): Iterates from start up to and including end.

main {
    print("Exclusive (1..5):")
    for i in 1..5 {
        print(i) // Prints 1, 2, 3, 4
    }

    print("Inclusive (1..=5):")
    for i in 1..=5 {
        print(i) // Prints 1, 2, 3, 4, 5
    }
}

3.3 Flow Control Keywords: break and continue

Inside loops, you can use break and continue statements to alter the normal flow of execution.

• break: Immediately exits the innermost loop. Execution continues with the statement immediately following the loop.
• continue: Skips the rest of the current loop iteration and proceeds to the next iteration (evaluating the loop's condition again for while loops, or fetching the next element for for..in loops).

main {
    print("Demonstrating break and continue:")
    let count = 0
    while count < 10 {
        count = count + 1

        if count == 3 {
            continue // Skip printing 3
        }

        if count == 7 {
            break // Exit loop when count reaches 7
        }

        print("Current count:", count)
    }
    print("Loop finished.")
}

Output of the above code:

Demonstrating break and continue:
Current count: 1
Current count: 2
Current count: 4
Current count: 5
Current count: 6
Loop finished.

Notice that 3 and 7 were not printed. 3 was skipped by continue, and the loop terminated before 7 could be printed due to break.

3.4 Best Practices for Control Flow

• Clarity over Cleverness: Aim for clear and readable control flow. Overly complex nested if statements or intricate loop conditions can be hard to understand and maintain.
• Avoid Infinite Loops: Always ensure while loop conditions eventually become false. Use break judiciously to prevent unintended infinite loops.
• Use for..in for Collections: When iterating over arrays or processing dictionary keys, for..in is generally more idiomatic and safer than manual index-based while loops.
• Early Exit with if: For functions, use if statements to handle edge cases or invalid inputs early, reducing nesting and improving readability.