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Practice Loops in C#

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Using a `foreach` Loop

7:28 with James Churchill

In this video, we'll review the solution to the first challenge and introduce our second challenge—using a `foreach` loop to implement a method that'll give us a way to find a single item in our Media Library.

Instructions

2nd Challenge

  1. Add a method named FindItem() to the MediaLibrary class.

    • The method should return a MediaType item and define a parameter of type string named criteria.
    • Use a foreach loop to loop through the items array contained within the MediaLibrary class.
    • Return the item whose Title property contains the provided criteria string parameter value.

  2. In the Program.cs file, search the media library for an item by calling the FindItem() method.

    • If an item is found, pass it into a call to the static MediaLibrary DisplayItem() method.
    • If an item isn't found, write the message "Item not found!" to the console.

Finding a String Within Another String

There are many ways in C# to test if a string is contained within another string. Here's one approach that makes use of the String.Contains() method.

var songTitle = "Row Row Row Your Boat";
Console.WriteLine(songTitle.Contains("Your")); // Outputs "true" to the console
Console.WriteLine(songTitle.Contains("your")); // Outputs "false" to the console

This examples demonstrates one potential issue with this approach: the Contains() method is case-sensitive. As a workaround, we can call ToLower() on both the search criteria and item title.

var songTitle = "Row Row Row Your Boat";
Console.WriteLine(songTitle.ToLower().Contains("Your".ToLower())); // Outputs "true" to the console
Console.WriteLine(songTitle.ToLower().Contains("your")); // Outputs "true" to the console

By forcing all of the characters to lowercase, we're eliminating any case-sensitivity issues.

Here's the documentation on both the Contains() and ToLower() methods:

Help

If you get stuck on any of the following topics or simply need a refresher, click on a topic in list below to view the associated video in the C# Objects course.

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    Welcome back! 0:00
    How did you do? 0:00
    Let's walk through my solution. 0:01
    In the MediaLibrary class, 0:03
    I stubbed out a method named, 0:08
    DisplayItems. 0:14
    Within the method body, I added a for loop. 0:24
    Remember that a for loop has three sections, 0:33
    the initializer, the condition and the iterator sections. 0:36
    The initilizer section is used to declare and initialize a local loop varible. 0:41
    I declared the variable of type int named, index, And initialized it to 0. 0:47
    This variable will be used to keep track of which array index we're 0:56
    currently accessing within the loop. 1:01
    The conditions section is used to determine when it's time to exit the loop. 1:03
    I use the expression index 1:08
    < _items.Length. 1:13
    This expression will be evaluated right before each loop iteration. 1:22
    The question, is the index variable less than the length of the _items array, 1:26
    will be asked. 1:32
    If yes, then the loop iteration is executed, 1:33
    otherwise the loop will be exited. 1:37
    And lastly, the iterator's section, which is used to define what 1:40
    happens after each loop iteration, I used the expression index++. 1:44
    The ++ operator, or the increment operator, 1:50
    increments or increases the operand or variable by one. 1:55
    After defining the initializer, condition, and iterator sections for 2:01
    the for loop, I turned my attention to the implementation of the loop body. 2:06
    To write each item's information to the console, 2:11
    using the console writeline method, we can use its display text property. 2:14
    But to get access to the display text property, 2:19
    we first need to cast the item to its subtype. 2:22
    You might remember though that we've already implemented a method that 2:25
    already does all of this. 2:29
    In the Progam.cs file, the Display method 2:33
    provides the behavior that we're looking for. 2:37
    Given that, I decided to move the Display method 2:43
    from the Program.cs file to the MediaLibray class. 2:48
    I selected the method and cut it to the clipboard. 2:54
    Then I switched back to the MediaLibrary class file, 3:00
    And pasted it from the clipboard, right below our DisplayItems method. 3:06
    I left the method as a static method but added the public access modifier. 3:18
    Making the method public will allow us to still call it from 3:23
    the Program.cs file Main method. 3:27
    But I decided to make the name of the method a little bit more descriptive. 3:29
    So instead of just Display, I changed it to DisplayItem. 3:36
    And I added a using directive for the system namespace. 3:44
    So I didn't have to change these calls to the console WriteLine method. 3:47
    Actually, after adding this using directive, 4:00
    we can also update our GetItemAt method. 4:02
    We no longer need System.here before the Console.WriteLine method call 4:10
    With the DisplayItem method added, I added a call within the for loop body. 4:22
    To get the reference to the item to display, I used the index local loop 4:32
    variable to get a reference to the array element at that index. 4:36
    _items, and then a pair of brackets, and 4:40
    then inside of the brackets, the index local loop variable. 4:44
    And that completed my implementation for the DisplayItems method. 4:53
    Then, back in the Program.cs file, I added a call to the DisplayItems method, 4:57
    right after writing the number of items to the console. 5:04
    Media library.DisplayItems();. 5:17
    And I commented out the DetectMediaType method calls. 5:22
    And removed the Display method calls. 5:30
    And lastly, I compiled and ran my program. 5:36
    And here's the expected output. 6:03
    Now that we have a method to display all of the items in our MediaLibrary, let's 6:09
    improve our program yet again, by adding another method to the MediaLibrary class. 6:13
    For the second challenge, add a method named, 6:19
    FindItem to the MediaLibrary class that returns a media type item and 6:22
    defines parameter of type string, named criteria. 6:26
    Within the method body, use a for 6:30
    each to loop throw the items array contained within the MediaLibrary class. 6:33
    And return the item whose Title property contains the provided criteria string 6:39
    parameter value, item, and defines a parameter of type string, named criteria. 6:44
    If you need a hint on how to check if a string value contains another 6:52
    string value, see the teacher's notes for 6:56
    a walk-through of one way to solve this problem. 6:59
    Then in the Program.cs file, test your work by searching the MediaLibrary for 7:02
    an item by calling the FindItem method. 7:08
    If an item is found, 7:11
    pass it into a call to the static MediaLibrary DisplayItem method. 7:12
    And if the item isn't found, write the message, "Item not found!" to the console. 7:18
    And that's the second challenge. 7:24
    See you in just a bit. 7:26

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