Array iteration with for and foreach in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main difference between for and foreach loops when iterating over an array in C#?

for loop uses an index to access array elements, allowing modification of elements and control over iteration.

foreach loop directly accesses each element without an index, is simpler, but does not allow modifying the array elements directly.

beginner

Write a simple for loop to print all elements of an integer array numbers.

for (int i = 0; i < numbers.Length; i++)
{
    Console.WriteLine(numbers[i]);
}

beginner

How does the foreach loop improve code readability when iterating arrays?

foreach hides the index management and directly gives each element, making the code shorter and easier to read.

intermediate

Can you modify elements of an array inside a foreach loop in C#? Why or why not?

No, you cannot modify the elements directly inside a foreach loop because the loop variable is read-only and represents a copy of the element.

beginner

What happens if you try to access an array element with an index outside its bounds in a for loop?

You get a System.IndexOutOfRangeException error because the index is invalid and outside the array limits.

Which loop is best when you need to modify elements of an array during iteration?

A for

B foreach

C while

D do-while

The for loop allows access by index, so you can modify array elements directly.

What does foreach loop provide when iterating an array?

A Only index

B Index and element

C Only element

D Neither index nor element

foreach gives you each element directly, without the index.

What property gives the length of an array in C#?

A Length()

B Length

C Size

D Count

Arrays have a Length property (no parentheses) to get their size.

What error occurs if you use an invalid index in a for loop?

A IndexOutOfRangeException

B NullReferenceException

C ArgumentException

D InvalidOperationException

Accessing outside array bounds throws IndexOutOfRangeException.

Which loop is simpler for just reading all elements without changing them?

A for

B do-while

C while

D foreach

foreach is simpler and clearer for reading elements.

Explain how to iterate over an array using both for and foreach loops in C#.

Think about how you count items versus how you just look at each item.

Describe when you would choose a for loop over a foreach loop for array iteration.

Consider if you need to change or just read the items.