For-in loop with collections in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a for-in loop used for in Swift?

A for-in loop is used to repeat a block of code for each item in a collection, like an array or dictionary.

beginner

How do you loop through all elements in an array named fruits using a for-in loop?

You write: <br>for fruit in fruits {<br> print(fruit)<br>}<br>This prints each fruit in the array one by one.

intermediate

Can you use a for-in loop to iterate over a dictionary in Swift? How?

Yes! You loop over key-value pairs like this:<br>for (key, value) in dictionary {<br> print("\(key): \(value)")<br>}

beginner

What happens if you use a for-in loop on an empty collection?

The loop body does not run at all because there are no items to go through.

intermediate

Why is a for-in loop preferred over a traditional while loop for collections?

Because it is simpler, safer, and less error-prone. It automatically goes through each item without needing to manage indexes.

Which of the following is the correct way to loop through an array numbers in Swift?

A for number; numbers { print(number) }

B for number in numbers { print(number) }

C for (number in numbers) { print(number) }

D loop number in numbers { print(number) }

Option B uses the correct Swift syntax for a for-in loop.

What does the variable in a for-in loop represent when looping over a dictionary?

A The index of each item

B Only the keys

C Only the values

D Each key-value pair as a tuple

In Swift, looping over a dictionary gives you each key-value pair as a tuple.

What will happen if you run a for-in loop on an empty array?

A The loop body does not execute

B The loop runs infinitely

C The loop runs once with a nil value

D The program crashes

The loop body does not run because there are no items to iterate over.

Which collection types can you use with a for-in loop in Swift?

A Arrays, dictionaries, sets, and ranges

B Only arrays

C Only dictionaries

D Only strings

Swift's for-in loop works with any collection type like arrays, dictionaries, sets, and ranges.

Why might you choose a for-in loop over a while loop when working with collections?

A For-in loops are more complex

B While loops are easier to read

C For-in loops automatically handle iteration safely

D While loops are faster

For-in loops automatically handle going through each item safely without manual index management.

Explain how a for-in loop works with an array in Swift. Include an example.

Think about how you say 'for each item in the list, do something'.

Describe how to use a for-in loop to iterate over a dictionary and access both keys and values.

Remember dictionaries store pairs, so you get two things each time.