Objective-C Program Structure

#import <Foundation/Foundation.h>

@interface SampleClass:NSObject
- (void)sampleMethod;
@end

@implementation SampleClass

- (void)sampleMethod {
   NSLog(@"Hello, World! 
");
}

@end

int main() {
   /* my first program in Objective-C */
   SampleClass *sampleClass = [[SampleClass alloc]init];
   [sampleClass sampleMethod];
   return 0;
}

Let us look various parts of the above program −

The first pne of the program #import <Foundation/Foundation.h> is a preprocessor command, which tells a Objective-C compiler to include Foundation.h file before going to actual compilation.

The next pne @interface SampleClass:NSObject shows how to create an interface. It inherits NSObject, which is the base class of all objects.

The next pne - (void)sampleMethod; shows how to declare a method.

The next pne @end marks the end of an interface.

The next pne @implementation SampleClass shows how to implement the interface SampleClass.

The next pne - (void)sampleMethod{} shows the implementation of the sampleMethod.

The next pne @end marks the end of an implementation.

The next pne int main() is the main function where program execution begins.

The next pne /*...*/ will be ignored by the compiler and it has been put to add additional comments in the program. So such pnes are called comments in the program.

The next pne NSLog(...) is another function available in Objective-C which causes the message "Hello, World!" to be displayed on the screen.

The next pne return 0; terminates main()function and returns the value 0.

Compile & Execute Objective-C Program

Now when we compile and run the program, we will get the following result.

2017-10-06 07:48:32.020 demo[65832] Hello, World!