Foreach loops

A foreach loop is a simpler way to iterate through all the elements in an array.

Its syntax is this:

foreach (type itemName in arrayName)
{
    // Use itemName here
}

The code above is equivalent to this:

for (int i = 0; i < arrayName.Length; i++)
{
    type itemName = arrayName[i];
    // Use itemName here
}

…but just shorter and easier to read.

Our example from before: sum of an array

Before, we used this code to find the sum of all the numbers in an array:

int[] numbers = { 10, 20, 30, 40, 50 };
int sum = 0;
for (int i = 0; i < numbers.Length; i++)
{
    sum += numbers[i];
}
Console.WriteLine(sum); // Output: The sum is: 150

We can rewrite this using a foreach loop like this:

int[] numbers = { 10, 20, 30, 40, 50 };
int sum = 0;
foreach (int number in numbers)
{
    sum += number;
}
Console.WriteLine(sum); // Output: The sum is: 150

Modifying items in an array with foreach

Importantly, you cannot use a foreach loop to modify the items in an array.

For example, the following code will not work as intended:

int[] numbers = { 10, 20, 30, 40, 50 };
foreach (int number in numbers)
{
    number *= 2; // This does NOT modify the array!
}

The reason this doesn’t modify the array is because number is a copy of the element in the array. That means that changing number does not change the original element in the numbers array, so we’re not actually modifying the array at all.

If you want to modify each element in an array, you need to use a regular for loop instead, like we had before:

int[] numbers = { 10, 20, 30, 40, 50 };
for (int i = 0; i < numbers.Length; i++)
{
    numbers[i] *= 2; // This DOES modify the array
}