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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.
+
+```cpp
+// 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 = %@", thirdNumber); // 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,", jj++);
+ } // => 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 instanceMethodWithParameter:@"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 called 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)