Code-Along: Speaking Grandma

Objectives

1. Convert a string to its uppercase version.
2. Capture the result of a comparison method into a BOOL variable.
3. Practice flow control by using an if/else statement.
4. Use the negation operator (!) to perform an inverted check.

Advanced

1. Change the compared objects after capturing the result of the comparison into a BOOL variable. See what happens.

Instructions

This code-along lab will walk you through creating an if/else statement, comparing strings, and creating a BOOL variable to pass into a conditional.

Open the objc-speaking-grandma.xcodeproj file and navigate to the FISAppDelegate.m implementation file. You'll enter all of your code in the application:didFinishLaunchingWithOptions: method body (between the curly braces {``} but before the return YES; statement).

Code-Along I: Talk To Grandma

1 — Create an NSString variable called talkToGrandma and set it equal to any regular sentence that you like:

• NSString *talkToGrandma = @"Hi, Grandma!";

2 — Create an NSString variable called shoutAtGrandma and set it equal to the result of calling the uppercaseString method on talkToGrandma:

• NSString *shoutAtGrandma = [talkToGrandma uppercaseString];

3 — Create a BOOL variable called shouting and set it equal to the result of comparing talkToGrandma and shoutAtGrandma with the isEqualToString: method:

• BOOL shouting = [talkToGrandma isEqualToString:shoutAtGrandma];
  Top-tip: Remember that BOOLs are declared without using a * symbol.

4 — Write an if statement that evaluates shouting as its conditional. If the if statement passes, print what Grandma says when she (thinks she) hears you: "NO, NOT SINCE 1938!" by using an NSLog():

if (shouting) {  
    NSLog(@"NO, NOT SINCE 1938!"); 
}

5 — Add an else statement that prints what Grandma says when she definitely can't hear you: "WHAT'S THAT? SPEAK UP, DEAR!" by using an NSLog():

if (shouting) {  
    NSLog(@"NO, NOT SINCE 1938!"); 
} else {
    NSLog(@"WHAT'S THAT? SPEAK UP, DEAR!");
}

• Run your program using ⌘ R to see how Grandma replies to what you said to her. If you didn't type your talkToGrandma string in all capitals, then you should see WHAT'S THAT? SPEAK UP, DEAR! printed to your console.

6 — Change your talkToGrandma string declaration to a sentence that's in all uppercase letters:

• NSString *talkToGrandma = @"HI, GRANDMA!";
• Run your program again using ⌘ R, you should now see NO, NOT SINCE 1938! printed to your console.

Code-Along II: Direct Evaluation

1 — Add a new version of your if/else statement that doesn't use the shouting boolean, but directly evaluates the result of comparing talkToGrandma with shoutAtGrandma using the isEqualToString: method:

if ([talkToGrandma isEqualToString:shoutAtGrandma]) {
    NSLog(@"NO, NOT SINCE 1938!");
} else {
    NSLog(@"WHAT'S THAT? SPEAK UP, DEAR!");
}

• Run your program again using ⌘ R, you should now see NO, NOT SINCE 1938! printed to your console.

2 — Change your talkToGrandma string declaration back to a regular sentence containing lowercase letters:

• NSString *talkToGrandma = @"Hi, Grandma!";
• Run your program again using ⌘ R, you should now see WHAT'S THAT? SPEAK UP, DEAR! printed to your console.

Code-Along III: Inverted Check

1 - Add a new version of your if/else statement from Code-Along I that uses the negation operator (!) to invert the evaluation of the shouting boolean. Switch the order of your NSLog()s so that Grandma still gives the appropriate reply:

if (!shouting) {
    NSLog(@"WHAT'S THAT? SPEAK UP, DEAR!");
} else {
    NSLog(@"NO, NOT SINCE 1938!");
}

• Run your program again using ⌘ R, you should still see WHAT'S THAT? SPEAK UP, DEAR! printed to your console.

2 - Add a new version of your if/else statement from Code-Along II that instead uses the negation operator (!) to invert the evaluation of the result of comparing talkToGrandma and shoutAtGrandma with the isEqualToString: method. Switch the order of your NSLog()s so that Grandma still gives the appropriate reply:

if (![talkToGrandma isEqualToString:shoutAtGrandma]) {
    NSLog(@"WHAT'S THAT? SPEAK UP, DEAR!");
} else {
    NSLog(@"NO, NOT SINCE 1938!");
}

• Run your program again using ⌘ R, you should still see WHAT'S THAT? SPEAK UP, DEAR! printed to your console.

3 — Change your talkToGrandma string one last time to an uppercase string (NSString *talkToGrandma = @"HI, GRANDMA!") and run the program using ⌘ R. You should see NO, NOT SINCE 1938! printed to your console.

Advanced

Immediately after declaring the shouting boolean and setting it to the return from the isEqualToString: method, redefine the talkToGrandma string back to your regular sentence containing lowercase letters. Also redefine shoutAtGrandma to capture the return of the same uppercaseString method call:

NSString *talkToGrandma = @"HI, GRANDMA!";
NSString *shoutAtGrandma = [talkToGrandma uppercaseString];
BOOL shouting = [talkToGrandma isEqualToString:shoutAtGrandma];

talkToGrandma = @"Hi, Grandma!";
shoutAtGrandma = [talkToGrandma uppercaseString];

Now run (⌘ R) your program again and see what happens. You should get different print outs by your if/else statements that evaluated the shouting boolean versus your if/else statements that directly evaluated the comparison with the isEqualToString: method:

NO, NOT SINCE 1938!            // boolean
WHAT'S THAT? SPEAK UP, DEAR!   // method

This is because the shouting boolean holds the evaluation of the isEqualToString: method from the point in our code at which it was last set. Since we changed the talkToGrandma and shoutAtGrandma strings after we set the shouting boolean, the result of directly comparing the strings will differ from the result that was captured into the shouting boolean above.

Booleans can be useful for preserving the result of a comparison from a particular point in your code for later use. But evaluating a boolean variable instead of the direct result of a comparison will not give you a "live" result based on the present state of your code.