1. Introduction to Objective C
By
Mayank Jalotra

2. INTRODUCTION
Objective-C was invented by Brad Cox and Tom Love.
Objective-C is a high-level, object-oriented programming language that
adds Smalltalk-style messaging to the C programming language
It is the main programming language used by Apple for the OS X
and iOS operating systems and their respective APIs, Cocoa and Cocoa Touch
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3. INTRODUCTION (Cont.)
Objective-C source files has a “.m” extension.
“.h” file is the interface file.
For example:
─ main.m
─ List.h (Interface of List class.)
─ List.m (Implementation of List class.)
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4. SYNTAX
Objective-C is a thin layer on top of C, and moreover is
a strict superset of C.
It is possible to compile any C program with an Objective-C
compiler.
Objective-C derives its object syntax from Smalltalk.
 All of the syntax for non-object-oriented operations are identical to
that of C
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5. Basic syntax structure
C++ syntax :
void function(int x, int y, char z);
Object.function(x, y, z);
Objective-C syntax :
-(void) function:(int)x, (int)y, (char)z;
[Object function:x, y, z];
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6. Keyword: id
 The word „id‟ indicates an identifier for an object
much like a pointer in c++.
 This uses dynamic typing.
 For example, if Pen is a class…
extern id Pen;
id myPen;
myPen = [Pen new ]; Mayank Jalotra

7. MESSAGES
To get an object to do something, you send it a message
telling it to apply a method. In Objective-C, message
expressions are enclosed in square brackets
[receiver message].
In Objective-C one does not simply call a method;
one sends a message
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8. Messages Cont.
 For example, this message tells the myRect object
to perform its display method, which causes the
rectangle to display itself
[myRect display];
[myRect setOrigin:30.0:50.0];
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9. HELLO WORLD
Hello World
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10. CODE EXPLAINATION [1]
CODE EXPLAINATION
 The parameter argc is the argument count at the time the
program is invoked. For example, if your program was called
“justarty” and you typed “justarty one two” into the command line
the computer would execute justarty.exe after passing “one” and
“two” into the program.
 The value stored in the program for argc would be 3 (including
the program name). The parameter argv on the other hand is the
actual array of arguments. In our example the array of arguments
would be
 argv[0] = “justarty”
 argv[1] = “one”
 argv[2] = “two”
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11. CODE EXPLANATION [2]
 NSAutoreleasePool * pool = [[NSAutoreleasePool
alloc] init];
• The NSAutoreleasePool is one of Cocoa's memory-
management tools.
 NSLog(@"Hello, World!");
 The NSLog function works very much like printf in the C
language. The difference is that NSLog takes an NSString
object instead of a C string. The @" . . . " construct is a
compiler directive that creates an NSString object using
the characters between the quotation marks.
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12. CODE EXPLANATION [3]
 [pool release];
• This line contains another part of Cocoa's memory
housekeeping
 return 0;
• A return from the main function indicating a normal program
exit
//NS stands for NeXTSTEP. All of the classes and functions in the Cocoa
frameworks start with NS.
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13. Example 1:
#import <Foundation/Foundation.h>
int main(int argc, const char* argv[]) {
NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];
NSLog (@”Hello World”);
int undergrads = 120;
int postgrads = 50;
int students = undergrads + postgrads;
NSLog (@”Now featuring...n %i Computer Science students”, students);
[pool drain];
return 0;
}
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14. INTERFACE
 The declaration of a class interface begins with the compiler
directive @interface and ends with the directive @end.
@interface ClassName : ItsSuperclass
{
instance variable declarations
}
method declarations
@end
─ Goes in source(.h) file
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15. IMPLEMENTATION
 The implementation of the class is done as :
#import <Foundation/Foundation.h>
#include “interfacename.h“
@implementation ClassName
define method function here;
define another method function here;
define yet another method function here;
@end
─ Goes in source(.m) file
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16. Example 2: ComputerScience.h
Example 3: ComputerScience.h
@interface ComputerScience : NSObject
{
int mUndergrads;
int mPostgrads;
}
-(void) print;
-(void) setUndergrads: (int) undergrads;
-(void) setPostgrads: (int) postgrads;
@end
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17. Example 2: ComputerScience.m
#include “ComputerScience.h”
@implementation ComputerScience
-(void) print {
int totalStudents = mUndergrads + mPostgrads;
NSLog (@”Total students in CompSci= %i”, totalStudents);
}
-(void) setUndergrads: (int) undergrads {
mUndergrads = undergrads;
}
-(void) setPostgrads: (int) postgrads {
mPostgrads = postgrads;
}
@end
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18. Data Structures
 Objective-C arrays are similar to C arrays, but you can initialize whole
array in a list.
 Or just a few indices of the array. The rest are set to 0.
 Or mix and match; the example will create an array of size [8].
int values[3] = { 3, 4, 2 };
char letters[3] = { 'a', 'c', 'x' };
float grades[100] = {10.0,11.2,1.1};
int array[] = {[3]=11,[2]=1,[7]=0};
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19. Arrays and Functions
 Arrays can be passed as arguments to functions.
 This function will print every integer in an array but it needs to also be
told how long the array is (arrayLength).
 Statements with hard-coded indices such as array[4] are potentially
dangerous.
void function(int array[], int arrayLength) {
int fourthValue = array[4];
for (int i = 0; i < arrayLength; i++) {
NSLog(@”%i”, array[i]; }
}
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20. References
Learning Cocoa with Objective-C By Apple Computer, Inc. , James
Duncan Davidson
Start Programming the Mac Using Objective-C By Bert
Altenberg, Alex Clarke
Objective-C for Absolute Beginners By Gary Bennett, Mitch Fisher, Brad
Lees
Various Authors. Wikipedia: the Free Encyclopedia
http://en.wikipedia.org
 http://stackoverflow.com/questions
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