Topic 3330 min readStructured Tutorial

C# foreach Loop Tutorial

Quick Answer

The C# foreach loop is used to iterate over each element in a collection or array without needing an index. It simplifies looping by automatically handling the enumerator, making code easier to read and less error-prone when processing sequences.

Learning Objectives

Explain the purpose of foreach Loop in a practical learning context.
Identify the main ideas, terms, and decisions involved in foreach Loop.
Apply foreach Loop in a simple real-world scenario or practice task.

Introduction

In C#, loops are essential for executing repetitive tasks efficiently. Among the various loop types, the foreach loop provides a simple way to iterate over collections and arrays.

This tutorial will explain how the foreach loop works, when to use it, and provide practical examples to help you master this fundamental concept.

Simplify iteration with foreach: Readable, safe, and efficient.

What is the foreach Loop?

The foreach loop in C# is designed to iterate over each element in a collection or array without manually managing the loop counter or index.

It automatically retrieves each element in sequence, making your code cleaner and less prone to errors.

Works with arrays, lists, and any collection implementing IEnumerable.
Does not allow modifying the collection during iteration.
Simplifies code by removing index management.

Syntax of foreach Loop

The basic syntax of the foreach loop includes specifying the type of elements, a variable name to represent each element, and the collection to iterate over.

foreach Loop Syntax
Component	Description
foreach	Keyword to start the loop
(type variable	Declares the loop variable representing each element
in collection)	Specifies the collection or array to iterate
{ ... }	Block of code executed for each element

Example: Iterating Over an Array

Here is a simple example demonstrating how to use foreach to iterate over an array of integers and print each value.

When to Use foreach Loop

Use foreach when you need to read or process each element in a collection without modifying the collection structure.

It is ideal for scenarios where the order of elements matters and you want to avoid errors related to index management.

Iterating over arrays and lists.
Processing elements in collections like dictionaries or sets.
When you do not need to modify the collection during iteration.

Limitations of foreach Loop

The foreach loop does not allow changing the collection size during iteration and does not provide direct access to the index of elements.

If you need to modify elements or access indices, consider using a for loop instead.

Cannot add or remove elements from the collection while iterating.
Loop variable is read-only; you cannot assign a new value to it.
No direct access to element indices.

Practical Example

This example prints each integer in the numbers array to the console using a foreach loop.

This example demonstrates iterating over a List of strings and printing each fruit name.

Examples

Iterating Over an Integer Array

int[] numbers = {1, 2, 3, 4, 5};
foreach (int number in numbers)
{
    Console.WriteLine(number);
}

This example prints each integer in the numbers array to the console using a foreach loop.

Iterating Over a List of Strings

List<string> fruits = new List<string> {"Apple", "Banana", "Cherry"};
foreach (string fruit in fruits)
{
    Console.WriteLine(fruit);
}

This example demonstrates iterating over a List of strings and printing each fruit name.

Best Practices

Use foreach when you only need to read elements without modifying the collection.
Prefer foreach for readability and simplicity over for loops when index is not required.
Avoid modifying the collection inside a foreach loop to prevent runtime exceptions.
Use descriptive variable names in the foreach loop for clarity.

Common Mistakes

Trying to modify the collection (add/remove elements) inside a foreach loop.
Attempting to change the loop variable inside the foreach block.
Using foreach when you need the index of elements; use for loop instead.
Assuming foreach works with non-iterable types.

Hands-on Exercise

Iterate and Print Array Elements

Write a C# program that uses a foreach loop to iterate over an array of strings and prints each string in uppercase.

Expected output: Each string printed in uppercase on a new line.

Hint: Use the ToUpper() method on each string inside the loop.

Sum Elements Using foreach

Create a program that sums all integers in an array using a foreach loop and prints the total.

Expected output: The sum of all integers printed to the console.

Hint: Initialize a sum variable before the loop and add each element inside the loop.

Interview Questions

What is the main difference between a for loop and a foreach loop in C#?

Interview

A for loop uses an index to iterate over elements and allows modifying the collection, while a foreach loop automatically iterates over each element without an index and does not allow modifying the collection during iteration.

Can you modify elements of a collection inside a foreach loop?

Interview

You cannot modify the collection structure (add/remove elements) inside a foreach loop, but you can modify the properties of the elements if they are reference types.

What is foreach Loop, and why is it useful?

Beginner

The C# foreach loop is used to iterate over each element in a collection or array without needing an index.