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Activity 3.4 Foreach Loops

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Introduction

Although while loops and for loops are capable of iterating through collections, there is another C# loop that makes iterating through collections very easy and intuitive. This loop is known as a foreach loop, and it’s purpose is to iterate through array elements in sequence, or one at a time.

Example

string[] fruits = new string[] { "apples", "bananas", "cherries", "dates" };

foreach (string fruit in fruits)
{
    Console.WriteLine("I like to eat " + fruit);
}

I like to eat apples
I like to eat bananas
I like to eat cherries
I like to eat dates

Notice the simplicity. No keeping track of i, no fear of accidentally trying to access an index that is out of range. As with the i variable and for loops, the declared variable is only accessible within the scope of the foreach loop.

Here is the rule for tracing foreach loops: for every element, perform one iteration. For every iteration, the foreach loop will assign the next element to the variable. So, the fruit variable is initially assigned the string "apple", then "bananas", and so on. Four elements yields four iterations.

For Loop vs Foreach Loop

You may be wondering if the foreach loop renders while and for loops obselete. The answer is a resounding no!

• When you need to access each element without modifications, use a foreach loop.
• When you need to modify, or change elements, consider a for loop or even a while loop, depending on your needs.

Foreach loops are not meant to modify the collection it’s iterating through, so I would consider a for loop in this case.

Skills to Practice

• Iterating through arrays using foreach loops
• Refactoring previous similar applications to use foreach loops where necessary

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Instructions

Setup

1. Create a new C# console application. Name the project 3.4 Foreach Loops.
2. Click Create.

Code

List<string> shoppingCart = new List<string>();
string input = "";

Console.WriteLine("--- Shopping Cart ---");

while (input != "3")
{
    Console.WriteLine("-Menu-");
    Console.WriteLine("1) Add item to shopping cart");
    Console.WriteLine("2) Display cart contents");
    Console.WriteLine("3) Exit");

    Console.Write("-> ");
    input = Console.ReadLine();

    if (input == "1")
    {
        Console.Write("Enter new item: ");
        input = Console.ReadLine();
        shoppingCart.Add(input);
    }
    else if (input == "2")
    {
        Console.WriteLine("\n-Cart Contents-");

        foreach (string item in shoppingCart)
        {
            Console.WriteLine($"- {item}");
        }
    }
    else if (input == "3")
    {
        Console.WriteLine("Exiting.");
    }
    else
    {
        Console.WriteLine("Invalid option. Please select again.");
    }

    Console.WriteLine();
}

Debug

--- Shopping Cart ---
-Menu-
1) Add item to shopping cart
2) Display cart contents
3) Exit
-> 1
Enter new item: Milk

-Menu-
1) Add item to shopping cart
2) Display cart contents
3) Exit
-> 1
Enter new item: Eggs

-Menu-
1) Add item to shopping cart
2) Display cart contents
3) Exit
-> 1
Enter new item: Cheese

-Menu-
1) Add item to shopping cart
2) Display cart contents
3) Exit
-> 2

-Cart Contents-
- Milk
- Eggs
- Cheese

-Menu-
1) Add item to shopping cart
2) Display cart contents
3) Exit
-> 3
Exiting.

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Tips, Tricks, and Reflection

• Foreach loops can also iterate through characters of a string in a very intuitive way. We’ll play around with this idea shortly.