Foreach Loops

The foreach loop provides the cleanest way to iterate over collections, arrays, and other enumerable types.

Basic foreach Syntax


csharp
1string[] fruits = { "Apple", "Banana", "Cherry" };
2
3foreach (string fruit in fruits)
4{
5    Console.WriteLine(fruit);
6}

Output


1Apple
2Banana
3Cherry

Syntax


csharp
1foreach (type variable in collection)
2{
3    // Use variable
4}

type: The type of elements in the collection
variable: A new variable that holds each element
collection: The array or collection to iterate over

Arrays with foreach


csharp
1int[] numbers = { 10, 20, 30, 40, 50 };
2
3foreach (int num in numbers)
4{
5    Console.WriteLine(num);
6}
7
8// Calculate sum
9int sum = 0;
10foreach (int num in numbers)
11{
12    sum += num;
13}
14Console.WriteLine($"Sum: {sum}");  // 150

Strings with foreach

Strings are sequences of characters:


csharp
1string message = "Hello";
2
3foreach (char c in message)
4{
5    Console.WriteLine(c);
6}
7// H
8// e
9// l
10// l
11// o

Count Vowels


csharp
1string text = "Hello World";
2int vowelCount = 0;
3
4foreach (char c in text.ToLower())
5{
6    if (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u')
7    {
8        vowelCount++;
9    }
10}
11
12Console.WriteLine($"Vowels: {vowelCount}");  // 3

Using var

Let the compiler infer the type:


csharp
1var colors = new[] { "Red", "Green", "Blue" };
2
3foreach (var color in colors)
4{
5    Console.WriteLine(color);
6}

foreach is Read-Only

You cannot modify collection elements directly in foreach:


csharp
1int[] numbers = { 1, 2, 3 };
2
3foreach (int num in numbers)
4{
5    // num = num * 2;  // Error! Cannot modify iteration variable
6}
7
8// To modify, use a for loop with index:
9for (int i = 0; i < numbers.Length; i++)
10{
11    numbers[i] = numbers[i] * 2;  // OK
12}

Don't Modify Collection During foreach

Adding or removing items during iteration causes errors:


csharp
1List<int> numbers = new List<int> { 1, 2, 3, 4, 5 };
2
3// DON'T DO THIS - causes InvalidOperationException
4// foreach (int num in numbers)
5// {
6//     if (num == 3)
7//         numbers.Remove(num);  // Error!
8// }
9
10// Instead, collect items to remove first:
11List<int> toRemove = new List<int>();
12foreach (int num in numbers)
13{
14    if (num == 3)
15        toRemove.Add(num);
16}
17foreach (int num in toRemove)
18{
19    numbers.Remove(num);
20}
21
22// Or use RemoveAll:
23numbers.RemoveAll(n => n == 3);

foreach vs for

When to Use foreach

Reading all elements in order
You don't need the index
Cleaner, more readable code

When to Use for

You need the index
You need to modify elements
You need to iterate in reverse
You need to skip elements


csharp
1string[] names = { "Alice", "Bob", "Charlie" };
2
3// foreach: simple iteration
4foreach (string name in names)
5{
6    Console.WriteLine(name);
7}
8
9// for: when you need the index
10for (int i = 0; i < names.Length; i++)
11{
12    Console.WriteLine($"{i + 1}. {names[i]}");
13}

Getting Index with foreach

If you need an index with foreach, use a manual counter or LINQ:


csharp
1string[] items = { "A", "B", "C" };
2
3// Manual counter
4int index = 0;
5foreach (string item in items)
6{
7    Console.WriteLine($"{index}: {item}");
8    index++;
9}
10
11// Using LINQ Select (more advanced)
12foreach (var (item, idx) in items.Select((value, i) => (value, i)))
13{
14    Console.WriteLine($"{idx}: {item}");
15}

Lists with foreach


csharp
1List<string> tasks = new List<string>
2{
3    "Buy groceries",
4    "Clean room",
5    "Do homework"
6};
7
8Console.WriteLine("To-Do List:");
9foreach (string task in tasks)
10{
11    Console.WriteLine($"  [ ] {task}");
12}

Dictionaries with foreach


csharp
1Dictionary<string, int> ages = new Dictionary<string, int>
2{
3    { "Alice", 25 },
4    { "Bob", 30 },
5    { "Charlie", 35 }
6};
7
8// Iterate key-value pairs
9foreach (KeyValuePair<string, int> pair in ages)
10{
11    Console.WriteLine($"{pair.Key}: {pair.Value}");
12}
13
14// Or using var for cleaner code
15foreach (var pair in ages)
16{
17    Console.WriteLine($"{pair.Key} is {pair.Value} years old");
18}
19
20// Or deconstruct
21foreach (var (name, age) in ages)
22{
23    Console.WriteLine($"{name} is {age}");
24}

Practical Examples

Find Maximum


csharp
1int[] scores = { 85, 92, 78, 95, 88 };
2int max = scores[0];
3
4foreach (int score in scores)
5{
6    if (score > max)
7    {
8        max = score;
9    }
10}
11
12Console.WriteLine($"Highest score: {max}");  // 95

Search for Item


csharp
1string[] names = { "Alice", "Bob", "Charlie", "Diana" };
2string searchFor = "Charlie";
3bool found = false;
4
5foreach (string name in names)
6{
7    if (name == searchFor)
8    {
9        found = true;
10        break;  // No need to continue searching
11    }
12}
13
14Console.WriteLine(found ? "Found!" : "Not found");

Combine Array Elements


csharp
1string[] words = { "Hello", "World", "from", "C#" };
2string sentence = "";
3
4foreach (string word in words)
5{
6    sentence += word + " ";
7}
8
9Console.WriteLine(sentence.Trim());  // Hello World from C#
10
11// Better: use string.Join
12string joined = string.Join(" ", words);
13Console.WriteLine(joined);  // Hello World from C#

Summary

In this lesson, you learned:

foreach provides clean syntax for iterating over collections
Syntax: foreach (type item in collection)
You cannot modify collection elements directly
Don't add/remove items during iteration
Use for loops when you need the index or need to modify
Works with arrays, strings, lists, dictionaries, and more

Next, we'll learn about break and continue for controlling loop execution.