Foreach loop over collections in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of a foreach loop in C#?

A foreach loop is used to iterate over each element in a collection, such as an array or list, without needing to manage the loop counter manually.

beginner

How does a foreach loop differ from a for loop?

A foreach loop automatically accesses each element in a collection one by one, while a for loop requires manual control of the index to access elements.

intermediate

Can you modify the elements of a collection inside a foreach loop in C#?

No, you cannot modify the elements directly inside a foreach loop because the loop variable is read-only. To modify elements, use a for loop or other methods.

beginner

Write a simple foreach loop to print all items in a string array named fruits.

Example:<br>

string[] fruits = {"apple", "banana", "cherry"};
foreach (string fruit in fruits) {
    Console.WriteLine(fruit);
}

intermediate

What types of collections can be used with a foreach loop in C#?

Any collection that implements IEnumerable or IEnumerable<T> can be used with foreach, including arrays, lists, dictionaries, and custom collections.

Which keyword is used to iterate over each element in a collection in C#?

A foreach

B while

C do

D switch

The foreach keyword is designed to loop through each element in a collection easily.

What happens if you try to modify the loop variable inside a foreach loop?

A It modifies the original collection element

B It skips the current iteration

C It causes a compile-time error

D It modifies a copy of the element only

The loop variable in a foreach loop is read-only. Attempting to assign a new value to it causes a compile-time error.

Which of these collections can be used with foreach?

A Array

B All of the above

C Dictionary

D List

All these collections implement IEnumerable and can be iterated with foreach.

What is the correct syntax to start a foreach loop over a collection named items?

A foreach (var item in items) { }

B foreach (items in var item) { }

C foreach item in items { }

D foreach (items : item) { }

The correct syntax is foreach (var item in items) { }, where item is the loop variable.

Can foreach be used to iterate over a string in C#?

A Only if converted to a char array first

B No, strings cannot be iterated

C Only in .NET 6 and later

D Yes, because a string is a collection of characters

Strings implement IEnumerable<char>, so you can use foreach to iterate over each character.

Explain how a foreach loop works in C# and when you would use it.

Think about how you would read items from a list one by one.

Describe the limitations of modifying collection elements inside a foreach loop and how to handle such cases.

Consider why the loop variable is a copy and what alternatives exist.