whiley Coyote

Objectives

1. Practice using loops.
2. Encounter an infinite loop situation.

Advanced

1. Use arc4random_uniform() to generate a value within a specified range.

Introduction

Whiley Coyote is chasing us so, like Road Runner, we need to make sure that we stay one step ahead of him! To help us out, Road Runner is waiting 50 steps away from us with an anvil ready to drop on Whiley Coyote and flatten him into the ground. This means that we need to run 51 steps to ensure we don't get hit by the anvil ourselves. For each step we take, let's imitate Road Runner by printing "Meep! Meep!" to the console.

Instructions

To track our steps, let's implement a do-while loop:

do {
    statements
} while (condition)

1. Open the whileyCoyote.xcodeproj file and navigate to the application:didFinishLaunchingWithOptions: method in the FISAppDelegate.m implementation file.
2. Write a do-while loop that NSLog()s "Meep! Meep!". Write YES inside the conditional ().

• Hit run (⌘``R) and watch and your console printouts. You've just created an infinite loop! Hit stop (⌘``.).

3. Declare an NSUInteger variable called steps before the do-while loop in order to count the steps. Start steps at 0 ("zero") and set the loop's conditional to pass if steps is less than or equal to 50.

• Hit run and watch your console printouts. It's an infinite loop again! That's because we're not incrementing our counter inside the loop so the conditional will keep passing forever.

4. Insert steps++; into the loop's implementation body beneath the NSLog(). This will add one to steps each time the loop runs.

• Hit run. You should see a total of 51 Meep! Meep!s. Hint: Instead of counting the Meep! Meep!s, think about how you can print the value of the steps integer along with each Meep! Meep!.

5. Whiley Coyote gets frustrated easily and pulls out a sign that reads "YOU'RE CUCKOO!" every ten steps or so.

• At the beginning of the loop, add an if statement that checks whether steps is an even factor of 10 and also greater than 0. Hint: Use the modulus operator % to calculate the remainder of dividing steps by ten.
• Insert an NSLog() that prints YOU'RE CUCKOO! into the if statement.
• Hit run. You should see YOU'RE CUCKOO! mixed into the Meep! Meep!s in your console output.

6. Immediately after this if statement, add a new if statement that checks when steps equals 50. Insert an NSLog() that prints a string describing the sound of the anvil falling on Whiley Coyote (e.g. @"SMASH!").

• Hit run. Your console output should end with:

...
Meep! Meep!
Meep! Meep!
YOU'RE CUCKOO!
SMASH!
Meep! Meep!

Advanced

Whiley Coyote is actually pretty clever despite constantly getting outsmarted by Road Runner. Now that he's expecting the anvil to drop on him after 50 steps, Road Runner says that we need to randomize our plan to drop the anvil.

1. Define a new NSUInteger anvil variable before the loop and set it equal to arc4random_uniform(25) + 26. This generates a random integer from 26 to 50. Replace the two occurrences of 50 in the conditionals with the anvil variable.

• Hit run a few different times. Notice that the Road Runner drops the anvil after a different number of steps each time.

2. Play around with the range of the anvil variable by changing the integers that affect the usage of arc4random_uniform().

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