Merge pull request #206 from YannickL/master

Objective-C documentation

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+---
+
+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>
+#import "MyClass.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 the program
+    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
+ 
+    // Use NSLog to print lines to the console
+    NSLog(@"Hello World!"); // Print the string "Hello World!"
+ 
+    ///////////////////////////////////////
+    // Types & Variables
+    ///////////////////////////////////////
+    
+    // Primitive declarations
+    int myPrimitive1  = 1;
+    long myPrimitive2 = 234554664565;
+    
+    // Object declarations
+    // Put the * in front of the variable names for strongly-typed object declarations
+    MyClass *myObject1 = nil;  // Strong typing
+    id       myObject2 = nil;  // Weak typing
+    // %@ is an object
+    // 'description' is a convention to display the value of the Objects
+    NSLog(@"%@ and %@", myObject1, [myObject2 description]); // Print "(null) and (null)"
+    
+    // String
+    NSString *worldString = @"World";
+    NSLog(@"Hello %@!", worldString); // Print "Hello World!"
+    
+    // Character literals
+    NSNumber *theLetterZNumber = @'Z';
+    char theLetterZ            = [theLetterZNumber charValue];
+    NSLog(@"%c", theLetterZ);
+
+    // Integral literals
+    NSNumber *fortyTwoNumber = @42;
+    int fortyTwo             = [fortyTwoNumber intValue];
+    NSLog(@"%i", fortyTwo);
+    
+    NSNumber *fortyTwoUnsignedNumber = @42U;
+    unsigned int fortyTwoUnsigned    = [fortyTwoUnsignedNumber unsignedIntValue];
+    NSLog(@"%u", fortyTwoUnsigned);
+    
+    NSNumber *fortyTwoShortNumber = [NSNumber numberWithShort:42];
+    short fortyTwoShort           = [fortyTwoShortNumber shortValue];
+    NSLog(@"%hi", fortyTwoShort);
+    
+    NSNumber *fortyTwoLongNumber = @42L;
+    long fortyTwoLong            = [fortyTwoLongNumber longValue];
+    NSLog(@"%li", fortyTwoLong);
+
+    // Floating point literals
+    NSNumber *piFloatNumber = @3.141592654F;
+    float piFloat           = [piFloatNumber floatValue];
+    NSLog(@"%f", piFloat);
+    
+    NSNumber *piDoubleNumber = @3.1415926535;
+    piDouble                 = [piDoubleNumber doubleValue];
+    NSLog(@"%f", piDouble);
+
+    // BOOL literals
+    NSNumber *yesNumber = @YES;
+    NSNumber *noNumber  = @NO;
+
+    // Array object
+    NSArray *anArray      = @[@1, @2, @3, @4];
+    NSNumber *thirdNumber = anArray[2];
+    NSLog(@"Third number = %@", thirdObject); // Print "Third number = 3"
+
+    // Dictionary object
+    NSDictionary *aDictionary = @{ @"key1" : @"value1", @"key2" : @"value2" };
+    NSObject *valueObject     = aDictionary[@"A Key"];
+    NSLog(@"Object = %@", valueObject); // Print "Object = (null)"
+
+    ///////////////////////////////////////
+    // Operators
+    ///////////////////////////////////////
+    
+    // The operators works like in the C language
+    // For example:
+    2 + 5; // => 7
+    4.2f + 5.1f; // => 9.3f
+    3 == 2; // => 0 (NO)
+    3 != 2; // => 1 (YES)
+    1 && 1; // => 1 (Logical and)
+    0 || 1; // => 1 (Logical or)
+    ~0x0F; // => 0xF0 (bitwise negation)
+    0x0F & 0xF0; // => 0x00 (bitwise AND)
+    0x01 << 1; // => 0x02 (bitwise left shift (by 1))
+
+    ///////////////////////////////////////
+    // Control Structures
+    ///////////////////////////////////////
+
+    // If-Else statement
+    if (NO)
+    {
+        NSLog(@"I am never run");
+    } else if (0)
+    {
+        NSLog(@"I am also never run");
+    } else
+    {
+        NSLog(@"I print");
+    }
+
+    // Switch statement
+    switch (2)
+    {
+        case 0:
+        {
+            NSLog(@"I am never run");
+        } break;
+        case 1:
+        {
+            NSLog(@"I am also never run");
+        } break;
+        default:
+        {
+            NSLog(@"I print");
+        } break;
+    }
+    
+    // While loops statements
+    int ii = 0;
+    while (ii < 4)
+    {
+        NSLog(@"%d,", ii++); // ii++ increments ii in-place, after using its value.
+    } // => prints "0," 
+      //           "1,"
+      //           "2,"
+      //           "3,"
+
+    // For loops statements
+    int jj;
+    for (jj=0; jj < 4; jj++)
+    {
+        NSLog(@"%d,", ii++);
+    } // => prints "0," 
+      //           "1,"
+      //           "2,"
+      //           "3,"
+     
+    // Foreach statements             
+    NSArray *values = @[@0, @1, @2, @3];
+    for (NSNumber *value in values)
+    {
+        NSLog(@"%@,", value);
+    } // => prints "0," 
+      //           "1,"
+      //           "2,"
+      //           "3,"
+
+    // Try-Catch-Finally statements
+    @try
+    {
+        // Your statements here
+        @throw [NSException exceptionWithName:@"FileNotFoundException" reason:@"File Not Found on System" userInfo:nil];
+    } @catch (NSException * e)
+    {
+        NSLog(@"Exception: %@", e);
+    } @finally
+    {
+        NSLog(@"Finally");
+    } // => prints "Exception: File Not Found on System"
+      //           "Finally"
+ 
+    ///////////////////////////////////////
+    // Objects
+    ///////////////////////////////////////
+    
+    // Create an object instance by allocating memory and initializing it.
+    // An object is not fully functional until both steps have been completed.
+    MyClass *myObject = [[MyClass alloc] init];
+        
+    // 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.
+    [myObject instanceMethodWithParmeter:@"Steve Jobs"];
+
+    // Clean up the memory you used into your program
+    [pool drain];
+    
+    // End the program
+    return 0;
+}
+
+///////////////////////////////////////
+// Classes And Functions
+///////////////////////////////////////
+
+// Declare your class in a header(MyClass.h) file:
+// Class Declaration Syntax:
+// @interface ClassName : ParentClassName <ImplementedProtocols>
+// {
+//    Member variable declarations;
+// }
+// -/+ (type) Method declarations;
+// @end
+@interface MyClass : NSObject <MyCustomProtocol>
+{
+    int count;
+    id data;
+    NSString *name;
+}
+// Convenience notation to auto generate public getter and setter
+@property int count;
+@property (copy) NSString *name; // Copy the object during assignment.
+@property (readonly) id data;    // Declare only a getter method.
+
+// Methods
++/- (return type)methodSignature:(Parameter Type *)parameterName;
+
+// + for class method
++ (NSString *)classMethod;
+
+// - for instance method
+- (NSString *)instanceMethodWithParmeter:(NSString *)string;
+- (NSNumber *)methodAParameterAsString:(NSString*)string andAParameterAsNumber:(NSNumber *)number;
+- 
+@end
+
+// Implement the methods in an implementation (MyClass.m) file:
+
+@implementation UserObject
+
+// Call when the object is releasing
+- (void)dealloc
+{
+}
+
+// Constructors are a way of creating classes
+// This is a default constructor which is call when the object is creating
+- (id)init
+{
+    if ((self = [super init]))
+    {
+        self.count = 1;
+    }
+    return self;
+}
+
++ (NSString *)classMethod
+{
+    return [[self alloc] init];
+}
+
+- (NSString *)instanceMethodWithParmeter:(NSString *)string
+{
+    return @"New string";
+}
+
+- (NSNumber *)methodAParameterAsString:(NSString*)string andAParameterAsNumber:(NSNumber *)number
+{
+    return @42;
+}
+
+// Methods declared into MyProtocol
+- (void)myProtocolMethod
+{
+    // statements
+}
+
+@end
+
+/*
+ * A protocol declares methods that can be implemented by any class.
+ * Protocols are not classes themselves. They simply define an interface
+ * that other objects are responsible for implementing.
+ * /
+@protocol MyProtocol
+    - (void)myProtocolMethod;
+@end
+
+
+
+```
+## 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)