Conditional Looping in Scala: Exploring `if` Statements and Loop Control Constructs

Lesson 4

Topic Overview

Welcome! Today, we're exploring Scala's special instructions: Conditional Looping, along with constructs that offer similar capabilities to Scala's break and continue. We know that loops enable code execution multiple times. Conditional looping, combined with Scala's powerful control constructs, enhances loop control, leading to flexible, efficient code. Put on your explorer's hat, and let's get started!

The 'if' Statement

Scala's if statement sets condition-based actions for your code. Consider this straightforward example where the if statement determines which message to print based on the value of temperature:

Scala
1object Solution {
2  def main(args: Array[String]): Unit = {
3    val temperature = 15
4
5    if (temperature > 20) {
6    println("Wear light clothes.") // This will print if temperature is over 20.
7    } else {
8    println("Bring a jacket.") // This will print otherwise.
9    }
10  }
11}

We can also evaluate multiple conditions using else if. In other words, "If the previous condition isn't true, then check this one":

Scala
1object Solution {
2  def main(args: Array[String]): Unit = {
3    if (temperature > 30) {
4      println("It's hot outside!") // Prints if temperature is over 30.
5    } else if (temperature > 20) {
6      println("The weather is nice.") // Prints if temperature is between 21 and 30.
7    } else {
8      println("It might be cold outside.") // Prints if temperature is 20 or below.
9    }
10  }
11}

The 'break' Statement

Scala doesn't have a direct break statement, but we can achieve similar functionality using scala.util.control.Breaks. Here’s how you can exit a loop prematurely when a condition is met:

Scala
1import scala.util.control.Breaks._
2
3object Solution {
4  def main(args: Array[String]): Unit = {
5    val numbers = List(1, 3, 7, 9, 12, 15)
6
7    breakable {
8      for (number <- numbers) {
9        if (number % 2 == 0) {
10          println(s"The first even number is: $number") // Prints the first even number.
11          break // Exits the loop after printing the first even number.
12        }
13        println(s"Number: $number")
14      }
15    }
16    // Prints:
17    // Number: 1
18    // Number: 3
19    // Number: 7
20    // Number: 9
21    // The first even number is: 12
22  }
23}

Alternatives to the 'continue' Statement

Scala doesn't have a continue statement, but we can achieve similar behavior using conditional expressions within the loop:

Scala
1object Solution {
2  def main(args: Array[String]): Unit = {
3    for (i <- 0 until 6) {
4      if (i != 3) {  // Skips the print statement for '3'
5        println(i) // Prints the numbers 0 to 5 except 3.
6      }
7    }
8    // Prints:
9    // 0
10    // 1
11    // 2
12    // 4
13    // 5
14  }
15}

Use-case with a For Loop

By integrating the tools we've discussed, you can write flexible loops. Here's how you would conclude a loop once you find "Charlie" using Scala:

Scala
1import scala.util.control.Breaks._
2
3object Solution {
4  def main(args: Array[String]): Unit = {
5    val names = List("Alice", "Bob", "Charlie", "David")
6
7    breakable {
8      for (name <- names) {
9        if (name == "Charlie") {
10          println("Found Charlie!") // Prints when 'Charlie' is found.
11          break // Stops the loop after finding Charlie.
12        }
13      }
14    }
15  }
16}

Lesson Summary and Practice

Congratulations! You are now more familiar with Scala's if statement, using breakable for loop control, and alternatives to continue statements, alongside their applications with loops. It's time to solidify your learning with upcoming practice exercises. Happy coding in Scala!

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