Libraries in C are split into two files, the interface, or header file (.h) and implementation (.m). The header tells the user what functionality is provided by the library. The implementation has the actual code. In this way it is easy to provide users with the interface files, and then give them a binary version of the library such that you can keep the implementation private.
Frameworks are a concept unique to OS X and iOS. Frameworks are
folders that group together headers, binaries, and documentation
for easy distribution. To see the various frameworks on your
system, open /System/Library/Frameworks from the Finder. Despite
looking like little legos, these are really just folders that
you can double click on and look inside. In the Hello World
program, we imported the Fondation framework with the line
@import Foundation;
System libraries are functionality that is outside of the C
language defintion but are considered part of the standard
language library. While much of the functionality of the C
standard library will be superceeded by iOS frameworks, we
do occasionally need to use the C standard librarys, for
example the math library.
#import <math.h>
Commands that start with the '#' character are known as
preprocessor directives. There are many of these, but
#import is the most common one we will use. The
angle brackets are what specify that this is a system library.
Custom libraries are code that we develop and want to reuse. They
are included almost identically to ystem libraries:
#import "console.h"
Note the quotation marks. This means that the compiler will look for
console.h in local paths.
math.h library. Write a program that will
print out the sin of a number
console.h and console.m files.
Add them to your project and import console.h. Update
your sin taking program to use user input