Steps

1. Using if clause as a statement

Let's declare two immutable integer variables namely numberOfPeople and donutsPerPerson. For simplicity, we are using Scala's type inference when declaring the variables which we have seen in the previous Type Inference tutorial. We then check if the numberOfPeople is greater than 10 and will print the number of donuts to be bought.

println("Step 1: Using if clause as a statement")
val numberOfPeople = 20
val donutsPerPerson = 2

if(numberOfPeople > 10)
  println(s"Number of donuts to buy = ${numberOfPeople * donutsPerPerson}")

NOTE:

• We are leveraging what we've learned from the Scala String Interpolation tutorial to help us build the String inside the println() function.

2. Using if and else clause as a statement

Now that we know how to write an if statement, let's extend the example from Step 1 and add an else clause to print a default number of donuts you need to buy if there is less that 10 persons.

println(s"\nStep 2: Using if and else clause as a statement")
val defaultDonutsToBuy = 8

if(numberOfPeople > 10)
  println(s"Number of donuts to buy = ${numberOfPeople * donutsPerPerson}")
else
  println(s"Number of donuts to buy = $defaultDonutsToBuy")

3. Using if, else if, and else clause as a statement

Let's extend once more our if statement to include and else if clause as follows:

println("\nStep 3: Using if, else if, and else clause as a statement")
if(numberOfPeople > 10) {
  println(s"Number of donuts to buy = ${numberOfPeople * donutsPerPerson}")
} else if (numberOfPeople == 0) {
  println("Number of people is zero.")
  println("No need to buy donuts.")
} else {
  println(s"Number of donuts to buy = $defaultDonutsToBuy")
}

NOTE:

• It's a good practice to enclose your if, else, else if statements with curly braces {} as they get more complex.

4. Using if and else clause as expression

What if you had to store the result of the if and else expressions above into a variable. With Scala, you can easily inline this as follows:

println("\nStep 4: Using if and else clause as expression")
val numberOfDonutsToBuy = if(numberOfPeople > 10) (numberOfPeople * donutsPerPerson) else defaultDonutsToBuy
println(s"Number of donuts to buy = $numberOfDonutsToBuy")

NOTE:

• In another language such as Java or .NET, you would have used the Ternary Operator to achieve Step 4.
• Perhaps Scala's functional style is much easier to read and less error prone compared to the ternary operator.