The foreach loop

Learn to iterate over collections with foreach.

The foreach loop

To walk through all elements of a collection in order you use foreach. The form foreach (var item in items) { ... } takes each element one by one; no counter or index is needed.

Array, list or any other collection does not matter; foreach uses the same pattern for all. It is read-only; you cannot modify the collection while iterating. So when you need to change it during the loop, prefer for.

foreach and readonly

In a foreach loop the loop variable is read-only; you cannot assign to it. A line like item = 5; raises a compile error. To modify elements, use for with an index.

This restriction is by design: foreach is meant to walk a collection safely and fast. When changes are needed, the pattern for (int i = 0; i < items.Length; i++) { items[i] = ...; } is the right approach.

Exercise Print names with foreach

Declare a names array: { "Alex", "Sam", "Kim" }. Use foreach to print each name with Console.WriteLine.

Show example solution

Write string[] names = { "Alex", "Sam", "Kim" }; foreach (var name in names) { Console.WriteLine(name); }
Example solution:
using System;

class Program
{
    static void Main()
    {
        string[] names = { "Alex", "Sam", "Kim" };
        foreach (var name in names)
        {
            Console.WriteLine(name);
        }
    }
}

Test yourself

What does foreach (var x in arr) Console.WriteLine(x); do?
```
int[] arr = {1, 2, 3};
foreach (var x in arr) Console.WriteLine(x);
```
- Prints each element of arr in order
- Prints only the first element
- Prints arr sorted
- Does nothing
Show answer

Prints each element of arr in order — Correct. foreach takes each element of the collection in order.
Match each foreach part to its meaning

foreach

Loop start
var item

Loop variable
in

Collection connector
items

Collection name

Write the foreach header

int[] nums = {10, 20, 30};
____ (var n in nums)
{
    Console.WriteLine(n);
}

Show answer

int[] nums = {10, 20, 30};
foreach (var n in nums)
{
    Console.WriteLine(n);
}

Next lesson: break and continue

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