MCQs on Control Structures | Scala

Explore key Scala concepts like if/else statements, loops (while, do-while, for-comprehensions), and pattern matching basics. These 30 MCQs will strengthen your understanding of Scala control structures.

Control Structures in Scala

1. If/Else Statements

1. How do you structure a simple if statement in Scala?
   • A) if (condition) { block }
   • B) if: condition -> block
   • C) if condition then block
   • D) if(condition); block
2. What is the return type of an if statement in Scala?
   • A) Always Boolean
   • B) Always Unit
   • C) Depends on the block’s result type
   • D) None
3. What happens if the else block is missing in a Scala if/else statement?
   • A) It throws an error
   • B) It assumes a default value of 0
   • C) It returns null
   • D) It returns () (Unit)
4. Which of the following is valid syntax for an if/else statement in Scala?
   • A) if (condition) block else block
   • B) if condition { block } else { block }
   • C) if (condition) { block } else { block }
   • D) All of the above
5. Can an if/else statement be used as an expression in Scala?
   • A) Yes
   • B) No
   • C) Only if it has an else block
   • D) Only in case classes

2. Loops: while, do-while, for-comprehensions

6. What is the primary difference between a while loop and a do-while loop?
   • A) while checks the condition after execution, do-while checks it before
   • B) do-while checks the condition after execution, while checks it before
   • C) while loops are faster
   • D) do-while loops do not require curly braces
7. What happens if the condition in a while loop is always true?
   • A) It runs indefinitely (infinite loop)
   • B) It throws a runtime error
   • C) It automatically exits after one iteration
   • D) It depends on the compiler
8. In a do-while loop, when is the condition checked?
   • A) Before the loop executes
   • B) After the loop executes once
   • C) Only if the loop executes more than once
   • D) It depends on the code
9. What is a key characteristic of a Scala for comprehension?
   • A) It can iterate over collections
   • B) It returns a new collection or value
   • C) It supports filtering with if clauses
   • D) All of the above
10. Which keyword is used in Scala to yield values from a for loop?
    • A) return
    • B) collect
    • C) yield
    • D) provide
11. Can for comprehensions in Scala include multiple if clauses?
    • A) Yes
    • B) No
    • C) Only one if clause is allowed
    • D) Only with nested loops
12. Which of the following best describes a guard in a for comprehension?
    • A) A condition to exit the loop early
    • B) A condition that filters iterations
    • C) A condition to initialize variables
    • D) A loop terminator
13. What is a valid example of a for comprehension with a guard in Scala?
    • A) for (x <- list if x > 0) yield x
    • B) for x in list where x > 0 yield x
    • C) for each x in list { if x > 0 yield x }
    • D) for x from list filter x > 0 yield x
14. Which loop structure is preferred for transforming collections in Scala?
    • A) while loop
    • B) do-while loop
    • C) for comprehension
    • D) foreach loop
15. Can a for comprehension in Scala use multiple generators?
    • A) Yes
    • B) No
    • C) Only with nested loops
    • D) Only when yielding lists

3. Pattern Matching Basics

16. What is pattern matching in Scala primarily used for?
    • A) Looping through collections
    • B) Defining constants
    • C) Matching values against patterns
    • D) Logging data
17. Which keyword is used to define pattern matching in Scala?
    • A) match
    • B) case
    • C) when
    • D) pattern
18. What is the default case in pattern matching?
    • A) else
    • B) case _
    • C) case *
    • D) default
19. What happens if no case matches in a pattern matching block?
    • A) A runtime exception is thrown
    • B) The program exits
    • C) The default case is executed automatically
    • D) It returns null
20. Can pattern matching be used as an expression in Scala?
    • A) Yes
    • B) No
    • C) Only in match blocks
    • D) Only with case classes
21. Which of the following supports pattern matching in Scala?
    • A) Case classes
    • B) Tuples
    • C) Sealed traits
    • D) All of the above
22. What does the underscore _ represent in pattern matching?
    • A) A wildcard pattern
    • B) An error condition
    • C) A default value
    • D) A null value
23. Can guards be used in pattern matching cases?
    • A) Yes
    • B) No
    • C) Only with tuples
    • D) Only with collections
24. Which of the following is a valid syntax for a match expression in Scala?
    • A) x match { case 1 => "one" case _ => "other" }
    • B) x match case 1 => "one" else "other"
    • C) match x: case 1 => "one"; _ => "other"
    • D) case x with 1 -> "one" default -> "other"
25. How are case classes useful in pattern matching?
    • A) They define unique object types
    • B) They automatically support deconstruction in matching
    • C) They can hold null values
    • D) They bypass default cases
26. What is required when using pattern matching with a sealed trait?
    • A) All cases must be defined
    • B) Only partial cases are allowed
    • C) It depends on the compiler
    • D) A wildcard case is mandatory
27. Can pattern matching be applied to collections in Scala?
    • A) Yes, using specific case patterns
    • B) No, it only works with primitive types
    • C) Yes, but only with immutable collections
    • D) Only for Lists
28. What is the purpose of case None in pattern matching?
    • A) Handles null values
    • B) Matches the absence of a value
    • C) Handles default cases
    • D) Matches all remaining cases
29. Which of the following is a valid example of tuple matching in Scala?
    • A) case (x, y) => x + y
    • B) match (x, y): x -> y
    • C) case x, y -> x + y
    • D) match case x + y
30. Can pattern matching be nested in Scala?
    • A) Yes
    • B) No
    • C) Only for case classes
    • D) Only for sealed traits

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