Objective-C for Absolute Beginners: iPhone, iPad, and Mac Programming Made Easy

340 Pages·2011·2.75 MB·English

by  Gary Bennett

CHAPTER 3: It’s All About the Data 51

Figure 3–11. Adding a bunny to our world
We need to declare a variable of type String. The variable will hold the string, “The sum
of 2 + 3 is:5”.
13. Click “Edit Code” in the bottom right of the scene to go back to our
Editor.
14. Select the Bunny instance. From the Procedures Tab, drag the this.bunny say
text:??? procedure tile to the editor. See Figure 3–12.
52 CHAPTER 3: It’s All About the Data

Figure 3–12. Adding the procedure (method) say to the editor
15. Click on Custom TextString and enter the string “The sum of 2 + 3 is:”
as the parameter value. See Figure 3–13.

Figure 3–13. Entering the string parameter
CHAPTER 3: It’s All About the Data 53
16. Click OK and then click on the first parameter for the say procedure.
Append the totalSum to our first parameter String. See Figure 3–14.

Figure 3–14. Adding the totalNumber to our customized string to display to the user
Alice did something very nice for us in the last step. It automatically converted the data
type totalSum from an integer to a string when it appended its value to the “The sum of
2 + 3 is:”. We will learn how to do this using Objective-C.
You can run the program now and will notice the customized string doesn’t display for
very long.
To increase the display time of our customized string, click on the option for a second
parameter of the say procedure and change the duration to 2 seconds or any other
value you like. See Figure 3–15.
54 CHAPTER 3: It’s All About the Data

Figure 3–15. The editor section
17. Press the play button and if you’ve done everything correctly, your app
should look like Figure 3–16 when it runs.

Figure 3–16. The app has run successfully!
Data Types and Objective-C
Now that we have covered the principles of data types and have written an Alice app to
help show how these principles apply, let’s write an Objective-C app that accomplishes
what we just did in Alice.
In Objective-C, we have similar data types as we did in Alice. Some of the most
frequently used data types for storing numbers are integers, doubles, floats, and longs.
CHAPTER 3: It’s All About the Data 55
Table 3–5 lists many of the basic data types. Many of these will be covered in later
chapters.
Table 3–5. Objective-C basic data types
Type Examples Specifiers
char ‘a’, ‘0’,’\n’ %c
int 42, -42, 550 0xCCE0, 099 %i, %d,
unsigned int 20u, 101U, 0xFEu %u, %x, %o
long int 13, -2010, 0xfefeL %ld,
unsigned long int 12UL, 100ul, 0xffeeUL %lu, %lx, %lo
long long int 0xe5e5e5LL, 501ll %lld
unsigned long long int 11ull, 0xffeeULL %llu, %llx, %llo
float 12.30f, 3.2e-5f, 0x2.2p09 %f, %e, %g, %a
double 3.1415, %f, %e, %g, %a
long double 3.1e-5l %Lf, %Le, %Lg, %La
id Nil %@
Our Objective-C app will add two integers and display their sum to the console. The app
will also display the text “The program has successfully terminated.” This will be fun and
easy, so let’s get started.
1. As iOS developers, Xcode is where we make our living, so open up
Xcode and create a new project. To do this, select File ➤ New project and
select the options shown in Figure 3–17. Click on Next.
56 CHAPTER 3: It’s All About the Data

Figure 3–17. Opening a new project
NOTE: One of the most common issues new students have when creating a command line app is
finding the project in their version of Xcode. Figure 3–18 shows Xcode Version 4.2 on the Lion
(10.7) operating system. Your version of Xcode may be newer or older and menus and selection
options may be different. So, look around in the File ➤ New project settings for the equivalent
options. If you have difficulty finding these options, visit our forum for this book at
forum.xcelme.com and go to this chapter. We will be happy to answer your questions.
2. Save the Product Name as Chapter 3 (see Figure 3–18). Then select the
directory to save your project and click on Next.
CHAPTER 3: It’s All About the Data 57

Figure 3–18. Project settings.
58 CHAPTER 3: It’s All About the Data

Figure 3–19. When created, and selecting the main.m file, your Xcode project should look this
3. After you create the project, you need to open your source code file in
your editor. Open the main.m source file. (see Figure 3–19)
If you haven’t seen “//” used in computer programming before, it enables the
programmer to comment about his or her code. Comments are not compiled by our
applications and are used as notes for the programmer or, more importantly, for
programmers who follow the original developer. Comments help both the original
developer and follow-up developers understand how the app was developed.
Sometimes, it is necessary for comments to span several lines or just part of a line. This
can be accomplished with the /* and the */. All the text between the /* and the */ are
treated as comments and are not compiled.
In our example, we first need to declare and initialize our variables firstNumber and
secondNumber. It is good practice to always initialize variables when they are declared or
soon afterwards.
We'll then increment the variables firstNumber and secondNumber by 1. We’ll print the
sum of firstNumber and secondNumber.
Finally, we will print to the console, “The program has terminated successfully.” See
Figure 3–20
CHAPTER 3: It’s All About the Data 59

Figure 3–20. Code for printing to the console
NSLog is a function that can take one or more parameters. The first parameter is
generally the string that is to be printed to the console. The @ symbol in front of the
string tells the compiler this is an Objective-C type string and not a C++ string. The @
symbol is typically used in front of all your strings for iPhone apps. If you don’t use
the @ symbol, you will probably get a compiler error. NSLog is a very helpful function used
by developers to test the execution of their code.
%d tells the compiler an integer will be printed and to substitute the value of the integer
for the %d. See Table 3–5 for other NSLog formatting specifiers. Finally, our second
parameter is the integer to be printed.
Figure 3–21 shows the completed executed output of our application.
To compile and run your application, click on the “Run” button on your toolbar. We can
see that we printed out the NSLog string along with the notice at the end by the debugger
saying the app's execution completed successfully.