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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>
// 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)
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