Loops in Scala

In this lesson, you will learn about loops in Scala. Loops allow you to execute a block of code multiple times until a condition is met.

Loops are essential when working with collections, performing repetitive tasks, and automating processes in programs.

Why Loops Are Important

Loops help you avoid writing the same code again and again. They are commonly used for:

• Iterating over lists and arrays
• Processing large amounts of data
• Repeating tasks until a condition is satisfied
• Building scalable logic

The for Loop

The for loop is the most commonly used loop in Scala. It iterates over a range or collection.

for (i <- 1 to 5) {
  println(i)
}

This loop prints numbers from 1 to 5. The expression 1 to 5 creates a range.

Using until in for Loop

The until keyword creates a range that excludes the last value.

for (i <- 1 until 5) {
  println(i)
}

This prints numbers from 1 to 4.

Looping Through Collections

Scala loops are commonly used with collections like lists.

val fruits = List("Apple", "Banana", "Orange")

for (fruit <- fruits) {
  println(fruit)
}

Each element of the list is accessed one by one.

for Loop with Conditions (Guards)

Scala allows you to add conditions inside loops using guards.

for (i <- 1 to 10 if i % 2 == 0) {
  println(i)
}

This prints only even numbers between 1 and 10.

Nested for Loops

You can nest loops to handle multi-level iterations.

for (i <- 1 to 3) {
  for (j <- 1 to 2) {
    println(s"i = $i, j = $j")
  }
}

Nested loops are useful for matrix operations and combinations.

for Loop as an Expression

In Scala, a for loop can also return a value. This is done using yield.

val squares = for (i <- 1 to 5) yield i * i
println(squares)

This creates a new collection containing the squares of numbers.

The while Loop

The while loop runs as long as a condition is true.

var count = 1

while (count <= 5) {
  println(count)
  count += 1
}

Use while loops carefully, as they rely on mutable variables.

The do–while Loop

The do–while loop executes the block at least once.

var num = 1

do {
  println(num)
  num += 1
} while (num <= 3)

Even if the condition is false, the loop runs once.

Best Practices for Loops

• Prefer for loops over while
• Use yield for transformations
• Avoid deeply nested loops when possible
• Use immutable collections when looping

📝 Practice Exercises

Exercise 1

Print numbers from 1 to 10 using a for loop.

Exercise 2

Print only odd numbers between 1 and 10.

Exercise 3

Create a list of cubes for numbers 1 to 5.

✅ Practice Answers

Answer 1

for (i <- 1 to 10) {
  println(i)
}

Answer 2

for (i <- 1 to 10 if i % 2 != 0) {
  println(i)
}

Answer 3

val cubes = for (i <- 1 to 5) yield i * i * i
println(cubes)

What’s Next?

In the next lesson, you will learn about Functions in Scala, which help you organize and reuse logic efficiently.