---

language: Objective-C
contributors:
    - ["Eugene Yagrushkin", "www.about.me/yagrushkin"]
    - ["Yannick Loriot", "https://github.com/YannickL"]
filename: LearnObjectiveC.m

---

Objective-C is the main programming language used by Apple for the OS X and iOS operating systems and their respective frameworks, Cocoa and Cocoa Touch.
It is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language. 

```Objective-C
// Single-line comments start with //

/*
Multi-line comments look like this.
*/

// Imports the Foundation headers with #import
#import <Foundation/Foundation.h>

// Your program's entry point is a function called
// main with an integer return type.
int main (int argc, const char * argv[])
{
    // Create an autorelease pool to manage the memory into your program
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
 
    // Use NSLog to print lines to the console
    NSLog(@"Hello World!"); // Print "Hello World!"
 
    // character literals
    NSNumber *theLetterZ = @'Z';

    // integral literals
    NSNumber *fortyTwo = @42;
    NSNumber *fortyTwoUnsigned = @42U;
    NSNumber *fortyTwoLong = @42L;
    NSNumber *fortyTwoLongLong = @42LL;

    // floating point literals
    NSNumber *piFloat = @3.141592654F;
    NSNumber *piDouble = @3.1415926535;

    // BOOL literals
    NSNumber *yesNumber = @YES;           // equivalent to [NSNumber numberWithBool:YES]
    NSNumber *noNumber = @NO;             // equivalent to [NSNumber numberWithBool:NO]

    // strings
    NSString *helloString = @"hello";

    // array
    NSArray *anArray = @[@1, @2];

    // dictionary
    NSDictionay *aDictionary = @{ @"key1" : @"value1", @"key2" : @"value2" };

    // Clean up the memory you used into your program
    [pool drain];
    
    // End your program
    return 0;
}

///////////////////////////////////////
// Classes And Functions
///////////////////////////////////////

// Declare your class in a header(.h) file:

@interface UserObject : NSObject
{
    // instance variables
}

// Class method
+ (NSString *)classMethod;

// Instance method
- (NSString *)instanceMethodWithParmeter:(NSString *)string;

@end

// Implement the methods in an implementation (.m) file:

@implementation UserObject

+ (NSString *)classMethod
{
    return @"SomeString";
}

- (NSString *)instanceMethodWithParmeter:(NSString *)string
{
    return @"New string";
}

- (NSNumber *)methodAParameterAsString:(NSString*)string andAParameterAsNumber:(NSNumber *)number
{
    return @42;
}

@end

// Create an object instance by allocating memory and initializing it. An object is not fully functional until both steps have been completed.
UserObject *someObject = [[UserObject alloc] init];

##Calling Methods

// The Objective-C model of object-oriented programming is based on message passing to object instances. 
// In Objective-C one does not simply call a method; one sends a message.

[someObject instanceMethodWithParmeter:@"Steve Jobs"];

##Nested Messages
// nested messages look like this:

[someObject instanceMethodWithParmeter:[someObject otherMethodWithString:@"Jony Ive"]];

```
## Further Reading

[Wikipedia Objective-C](http://en.wikipedia.org/wiki/Objective-C)

[Learning Objective-C](http://developer.apple.com/library/ios/referencelibrary/GettingStarted/Learning_Objective-C_A_Primer/)

[iOS For High School Students: Getting Started](http://www.raywenderlich.com/5600/ios-for-high-school-students-getting-started)