review of Structs Creating iOS 5 Apps, Develope and design

objectiveC-StructReview.m

/*
  Structs are the most flexible C data type
  can combine different types of data, access that data using named fields
  makes heavy use of C Structures -- many Core Frameworks in ObjC are written in pure C
*/

struct CGPoint {
  CGFloat x;
  CGFloat y;
};
typedef struct CGPoint CGPoint; // alias for CGPoint struct
                              

/* 1. Framework creates structure called CGPoint
*   Structure has 2 fields, x and y
*   Both fields happen to be the same data type (CGFloat)
*/

// the typedef enables us to avoid constantly referring to the entity as "struct CGPoint" in our code.
// now we can ddrop struct and treat it like any other data type

CGPoint pixelA;   // creates CGPoint variable
pixelA.x = 23.5;  // sets the x field
pixelA.y = 32.6;  // sets the y field
int x = pixelA.x; // reads the value from the x field

// for any struct type Apple provides convenience method for creating the struct, a method for comparing structs, methods to perform common 
// operations with the struct. for CGPoint these include CGPointMake(), CGPointEqualToPoint() and CGRectContainsPoint()


// 3 approaches to creating a CGRect. all equivalent
CGRect r1;

r1.origin.x=5;
r1.origin.y=10;
r1.size.width=10;
r1.size.height=20;
CGRect r2 = CGRectMake(5, 10, 10, 20);

// struct literal - each pair of curly braces represents a struct
CGRect r3 = {{5,10}, {10,20}};