1. Apply what you've learned about collections to correctly store some real-world information.
2. Verify that a dictionary contains the expected keys.
3. Retrieve a stored dictionary by the value for a key.

We're going to work towards building an app to allow users to share trivia facts about locations around the city. As users walk around, they can be notified of nearby trivia items. Before we get to work with trivia, we need to handle the data about nearby locations.

In this exercise, we're going to start by handling some data about a few locations in New York City. We're going to save the location's name, latitude, and longitude as values in a dictionary. In Objective-C, a manual declaration of such a dictionary would look like this:

NSDictionary *flatironSchool = @{ @"name": @"The Flatiron School",
                                  @"latitude": @34.432,
                                  @"longitude": @-23.67 };

Navigate to the FISAppDelegate.h header file and declare the following methods. Set them to return nil in the FISAppDelegate.m implementation file. Run the tests to see that most of them fail.

• stringByTruncatingNameOfLocation:toLength: that takes two arguments, an NSDictionary called location and an NSUInteger called length; and returns an NSString.

• dictionaryForLocationWithName:latitude:longitude: that takes three arguments, an NSString called name, and two CGFloats called latitude and longitude; and returns an NSDictionary.

• namesOfLocations: that takes one NSArray argument called locations and returns an NSArray.

• dictionaryIsValidLocation: that takes one NSDictionary argument and returns a BOOL.

• locationNamed:inLocations: that takes two arguments, an NSString called name and an NSArray called locations; and returns an NSDictionary.

Now, write out the method bodies for each method one by one. Run the tests each time you finish a method to check your work. Reference each of the tests to know what they're expecting.

1. stringByTruncatingNameOfLocation:toLength: should return a string containing the beginning of the submitted location's name with the number of letters specified in the length argument.
   Hint: Look up the substringToIndex: method on NSString.

2. dictionaryForLocationWithName:latitude:longitude: should return a dictionary containing the three argument values stored to keys of the argument names (@"name", @"latitude", @"longitude").

3. namesOfLocations: should return an array containing all of the values for the name key in the location dictionaries in the submitted locations array.

4. dictionaryIsValidLocation: should return YES only if the submitted location dictionary has exactly three keys by the names of @"name", @"latitude", and @"longitude". If any of these conditions fail, the method should return NO.
   Advanced: Write additional checks to determine that the value for latitude falls between -90.0 and 90.0, that the value for longitude falls between 180.0 and -180.0, and that the value for name is not an empty string. However, there are no tests for these cases.

5. locationNamed:inLocations: should return the location dictionary in the submitted locations array with the matching value for the name key as the submitted name string. If there are no matches, then it should return nil.