Learn Object C(1) Learn Objective-C in Day 6 - 1 ~ 3

What is Objective-C
Objective-C is a strict superset of C, we are free to use C in an Objective-C file and it will compile fine.

What will I need?
Since I installed Xcode on my MAC, I already have GCC.

Compiling your code
Open the MAC terminal and go to the work directory.
>cd /Users/carl/work/objective-c
>vi First.m
#include <stdio.h>
int main(){
    printf("Hello World\n");
    return 0;
}

>gcc First.m -o First
The system will compile the codes in First.m to machine codes into First.

Then I can run the codes with these commands>
>./First

I can get the println Hello World. I am a good student when I was in university while studying the C language.
That should be awesome to study objective-c from my understanding.

The Basics
int main(){
    printf("Hello World\n");
    return 0;
}

By convention, returning '0' signals to the calling program that our program finished execution without any errors.

Variables
int - for storing integers with no decimal point
char - for storing a character
float - for storing numbers with decimal points
double - same as float but double the accuracy

If we are not using variables, we are using constants. For instance, 123 + 2 = 125

Almost the same way of C language>
#include <stdio.h>
int main(){
     int someNumber = 123;
     printf("My number is %i \n", someNumber);
     return 0;
}

%i integer, %f float, %e double, %c char

Conditionals
int main(){
     if(1 == 1){
          //...snip...
     }
     return 0;
}

Loops
for (x = 0; x < 9; x++){
     printf("Count is: %i\n", x);
}

while ( x < 10){
     x++;
     printf("Count is: %i\n", x);
}

do {
     x++;
     printf("Count is: %i\n", x);
} while(x < 10);

Pointers
Pointers point to a location. Specifically, locations in computer memory. We have a variable named foo with value 123, we can also have a point points to foo.
int foo = 123;
int *ptr = &foo;

Wrapping Up
…snip…

Object Orientated Programming
Classes are made up of methods and attributes.

Interface and Implementation
Interface is a file that ends with a suffix of .h. Implementation is a file that ends with a suffix of .m.

Interface
@interface Car: NSObject 
@property (weak, nonatomic) IBoutlet UILabel *display;
- (void) addGas;
@end

Car is extends from Object NSObject

The "-" indicates that this is an instance method, not a class method.

Implementation
#import "Car.h"
@implementation Car
- (void) addGas {
}
@end

Classes from Apple
NS is abbreviation for NextStep.

NSString     immutable string
NSMutableString      mutable string
NSArray      immutable array
NSMutableArray       mutable array
NSNumber

Pointers and Initializing
File --> New Project ---> Mac OS X--> Application ---> Command Line Tool ----> Type: Foundation
#import <Foundation/Foundation.h>

int main(int argc, constchar * argv[]) {   

NSString *testString;                  

//pointer to NSString   

testString = [[NSString alloc] init];  

//have instance of NSString   

testString = @"sillycat test String";  

//@ a sign of NSString   

NSLog(@"only string= %@",testString);  

//%@ means an Objetive-C object   

return 0;
}

Inheritance
NSObject ---> NSString ----> NSMutableString
               ---> NSArray -----> NSMutableArray
               ---> NSValue -----> NSNumber


References:
http://www.otierney.net/objective-c.html.zh-tw.big5
http://developer.apple.com/library/ios/#referencelibrary/GettingStarted/Learning_Objective-C_A_Primer/_index.html
http://developer.apple.com/library/ios/#referencelibrary/GettingStarted/RoadMapiOS/chapters/Introduction.html
http://mobile.tutsplus.com/tutorials/iphone/learn-objective-c-day-1/

http://mobile.tutsplus.com/tutorials/iphone/learn-objective-c-2/
http://mobile.tutsplus.com/tutorials/iphone/learn-objective-c-day-3/
http://mobile.tutsplus.com/tutorials/iphone/learn-objective-c-day-4/

Objective C Book from Apple
https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/Introduction/Introduction.html

Android开发要用到NDK，装了一个虚拟机，老是不行。 后来安装了一个cygwin，安装完毕后unset home，再export NDK，就可以使用了，非常方便，不用像虚拟机那样经常切换。