01-First Knowledge OC

I. introduction of OC

1. based on the C language, a minimal object-oriented syntax is added

2. fully compatible with C language

3. You can mix C language code in OC code , even C + + code

4. applications that can use OC to develop Mac platforms and IOS platforms

Second,OC Common grammar

1. Keywords

* basically all keywords start with @

  @interface ,  @implementation , Span style= "color: #0000ff;" > @end   @public ,  @protected ,  @private  , @selector   @try ,  @catch ,  @throw ,  @finally   @protocol , @optional, @required,  @class   @property,   @synthesize  , @dynamicself, Super,  id , _cmd, __block, __strong, __weak, 

2. strings are preceded by @

@ "Hello" is a string in OC, while "Hello" is a string in the C language

3. Other Syntax

Third, the development process of OC program

Four, the first OC program

1. Code writing

#import <Foundation/Foundation.h>int  main () {    NSLog (@ " 2nd OC Program ");     return 0 ;}

2. Terminal Instructions

* compile cc-c code . M // code here . M for files with the extension. m

* link cc code . O-framework Foundation

* run . /A. Out

3. The difference between NSLog and printf

* NSLog receives OC string as parameter,printf receives C language string as parameter

* NSLog will be wrapped after output and will not be wrapped automatically after printf output .

* #import <Foundation/Foundation.h> required to use NSLog

* using printf requires #include <stdio.h>

4. The role of #import

* like #include , used to copy the contents of a file

* can automatically prevent the file content to be copied multiple times, it means that the header file is not included in the following preprocessing instructions

#ifndef _stdio_h_ #define _stdio_h_#endif

5. Role of the Foundation framework

* Develop The necessary framework for OC, IOS and MAC programs

* This framework contains a number of commonly used APIs(application programming interfaces)

* The framework contains a lot of header files, if you want to use the contents of the entire framework, including its main header file can be

#import <Foundation/Foundation.h>

6. use of BOOL

* variables of type BOOL have 2 values:YES,NO

#define YES (BOOL) 1#define NO  (bool) 0

* output of BOOL (as integer )

NSLog (@ "%d%d", YES, NO);

01-First Knowledge OC