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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 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;
long myPrimitive2;
// Object declarations
// Put the * in front of the variable names for strongly-typed object declarations
MyClass *myObject1; // Strong typing
id myObject2; // 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
///////////////////////////////////////
// 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(.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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