OC Language Learning (i) Hello world

. h : Header file. Header files contain declarations of classes, types, functions, and constants.  

. M : source code file. This is a typical source code file extension that can contain objective-c and C code.  

. MM : source code file. Source code files with this extension can contain C + + code in addition to the objective-c and C code. This extension is only used when you really need to use C + + classes or features in your objective-c code.

You can use standard #include compilation options when you need to include header files in your source code, but objective-c provides a better approach. The #import option is identical to the #include option, except that it ensures that the same file will only be included once.

#import <Foundation/Foundation.h>

OC recommended with #import contains header files, C-language method of # include can also

Foundation Framework

The include file is the same as C, and the user of the <> system

Key words

@interface,@implementation,@end

@public, @protected,@private,@selector

@try,@catch,@throw,@finally

@protocol,@class

Self, id, super, _cmd, _block, _strong, _weak (does not start with @)

The new keywords introduced in OC 2.0 have

@property,@synthesize

@optional,@required,@dynamic

The program entry is also a main function
The nslog function is defined as the form of C .

is a log output function that outputs incoming OC string parameters to the console

Automatic line wrapping after output is complete

Support for format characters:

*%f means to receive floating-point data,%.2f means to retain 2 decimal places

The format of the NSLog is as follows:

%@	Object
%d,%i	integer
%u,%z	No character shaping
%f	floating point / double word
%x,%x	hexadecimal integer
%o	octal integer
%zu	size_t
%p	pointer
%e	floating / double word (scientific calculation)
%g	floating point / double word
%s	c character String
%.*s	pascal string
%c	character
%c	unichar
%lld	64 bit long integer ( long Long
%llu	no 64 bit long integer
%lf	64 bit double word
%hhd	BOOL Boolean type

NSLog (@ "Hello World");//The string starts with @ in OC

#import <foundation/foundation.h>int Main () {    NSLog (@ "Hello world");    return 0;}

OC Language Learning (i) Hello world