- 2.1 Conditional Expressions
- 2.2 Statement Termination
- 2.3 Block Expressions and Assignments
- 2.4 Input and Output
- 2.5 Loops
- 2.6 Advanced for Loops and for Comprehensions
- 2.7 Functions
- 2.8 Default and Named Arguments L1
- 2.9 Variable Arguments L1
- 2.10 Procedures
- 2.11 Lazy Values L1
- 2.12 Exceptions
- Exercises
This chapter is from the book
This chapter is from the book
This chapter is from the book
2.5 Loops
Scala has the same while and do loops as Java and C++. For example,
while (n > 0) {
r = r * n
n -= 1
}
Scala has no direct analog of the for (initialize; test; update) loop. If you need such a loop, you have two choices. You can use a while loop. Or, you can use a for statement like this:
for (i <- 1 to n) r = r * i
You saw the to method of the RichInt class in Chapter 1. The call 1 to n returns a Range of the numbers from 1 to n (inclusive).
The construct
for (i <- expr)
makes the variable i traverse all values of the expression to the right of the <-. Exactly how that traversal works depends on the type of the expression. For a Scala collection, such as a Range, the loop makes i assume each value in turn.
When traversing a string or array, you often need a range from 0 to n – 1. In that case, use the until method instead of the to method. It returns a range that doesn’t include the upper bound.
val s = "Hello" var sum = 0 for (i <- 0 until s.length) // Last value for i is s.length - 1 sum += s(i)
In this example, there is actually no need to use indexes. You can directly loop over the characters:
var sum = 0 for (ch <- "Hello") sum += ch
In Scala, loops are not used as often as in other languages. As you will see in Chapter 12, you can often process the values in a sequence by applying a function to all of them, which can be done with a single method call.