Neal Goldstein

Cheat Sheet / Updated 03-23-2022

When you write an Objective-C program for your iOS or Mac OS X apps, all you're doing is providing a set of instructions for the computer to follow. Fundamentally, programs manipulate numbers and text, and all things considered, a computer program has only two parts: variables (and other structures), which "hold" the data, and instructions, which perform operations on that data. This Cheat Sheet provides some of the main aspects of Objective-C programming, including making a statement, built-in and new data types, operators, and more.

Article / Updated 03-26-2016

Programming iOS and Mac OS X apps in Objective-C is about making a statement. You can recognize a statement in Objective-C immediately by noting the semicolon at the end: statement; You will see other lines of code, but unless the line ends with a semicolon, it is not an Objective-C statement.

Article / Updated 03-26-2016

In programming, as in life, you have to make decisions and act on them. Objective-C provides control statements and loops to help your program take action. You may want to repeat a set of instructions based on some condition or state, for example, or even change the program execution sequence. Here is the basic syntax for Objective-C control statements and loops. if else <b>if</b> (condition) { statement(s) if the condition is true; } <b>else</b> { statement(s) if the condition is not true; } for <b>for</b> (counter; condition; update counter) { statement(s) to execute while the condition is true; } for in <b>for</b> (Type newVariable <b>in</b> expression ) { <b> </b> statement(s); } or Type existingVariable ; for (existingVariable in expression) { statement(s); } *Expression is an object that conforms to the NSFastEnumeration protocol. An NSArray and NSSet enumeration is over content. An NSDictionary enumeration is over keys. An NSManagedObjectModel enumeration is over entities. while while (condition) { statement(s) to execute while the condition is true } do while do { statement(s) to execute while the condition is true } while (condition); Jump statements return ; Stop execution and return to the calling function. break; Leave a loop. continue; Skip the rest of the loop and start the next iteration. goto labelName; ... labelName: An absolute jump to another point in the program (don't use it). exit(); Terminates your program with an exit code.

Article / Updated 03-26-2016

Objective-C operators, like those in other programming languages, let you perform operations on variables (hence the name). Objective-C provides many operators, and keeping track of all of them can be difficult as you program your iOS or Mac OS X apps. Use the following tables to jog your memory as to which operator accomplishes what task. Arithmetic Operators Operator What It Does + Addition - Subtraction * Multiplication / Division % Modulo Relational and Equality Operators Operator What It Does == Equal to != Not equal to > Greater than < Less than >= Greater than or equal to <= Less than or equal to Logical Operators Operator What It Does ! NOT && Logical AND || Logical OR Compound Assignment Operators Operator What It Does += Addition -= Subtraction *= Multiplication /= Division %= Modulo &= Bitwise AND |= Bitwise Inclusive OR ^= Exclusive OR <<= Shift Left >>= Shift Right Increment and Decrement Operators Operator What It Does ++ Increment -- Decrement Bitwise Operators Operator What It Does & Bitwise AND | Bitwise Inclusive OR ^ Exclusive OR ~ Unary complement (bit inversion) << Shift Left >> Shift Right Other Operators Operator What It Does () Cast , Comma Sizeof() Size of ? : Conditional & Address * Indirection

Article / Updated 03-26-2016

The variables you declare in Objective-C — Objective-C data types — must be a type that the compiler can recognize. Objective-C comes with a number of built-in data types, as well as mechanisms to create new ones, for programming your iOS or Mac OS X applications. Built-In Types Type Description Size char A character 1 byte int An integer — a whole number 4 bytes float Single precision floating point number 4 bytes double Double precision floating point number 8 bytes short A short integer 2 bytes long A double short 4 bytes long long A double long 8 bytes BOOL Boolean (signed char) 1 byte Enumeration types <span class="code">enum typeName { identifier1, ... identifiern};</span> Identifiers are of constants of type int. typedef typedef typeName identifier; Associates an identifier with a specific type. Constants const type identifier = value; #define identifier value Allows you to define names for constants.

Article / Updated 03-26-2016

Object-oriented programming languages enable you to declare classes, create derived classes (subclass), and send messages to the objects instantiated from a class. This is the essence of object-oriented programming and part of the object-oriented extensions that Objective-C adds to C. To ensure that everything operates smoothly, compiler directives are available that enable you to inform the compiler of your classes by using @class and #import. Interface #import "Superclass.h" @interface ClassName : Superclass { instance variable declarations; } method declarations @property(attributes) instance variable declaration; –d Implementation #import "ClassName.h" @implementation ClassName @synthesize instance variable ; method definitions –d Message Syntax [receiver message] #import #import "filename.h" Guarantees that a header file will be included only once. @class @class ClassName; Clues the compiler into user defined types.