#Constants and Variables

Swift- You can declare constants using let keyword and variables using var keyword in Swift. For example,

let name = "John" //declare constant
var loginAttempt: Int //declare variable
loginAttempt = 1 //assign number to variable

Objective-C- There are several types of constants in Objective-C but commonly used constants are numeric, string and bool. For example,

const int MAX_ATTEMPT = 5; //numeric constant
NSString const *name = @"John"; //string constant
const BOOL IS_EMAIL_VALID = YES; //bool constant

NSNumber *loginAttempt; //declare variable
loginAttempt = 1; //assign number to variable

#Properties

Swift- In Swift, classes and structs can define there own constants and variables and its called properties. These properties can be either stored or computed.

struct Employee {
 let name: String //declare constant stored property
 var salary: Int //declare variable stored property
 lazy var login = Login() // declare lazy property
}

For computed property, it can be either get or set to make action happens. For example, we add bonus property which automatically returns salary with bonus.

struct Employee {
 let name: String //declare constant stored property
 var salary: Int //declare variable stored property
 lazy var login = Login() // declare lazy property
 //read only property
 var bonus: Int {
  get {
    return salary * 2000
  }
 }
}

Objective-C- In Objective-C property declaration starts with @property keyword.

@property NSString *name; // declare simple property
@property (readonly) NSString *lastName; //declare readonly property
@property(readwrite) NSInteger salary; //declare read write property

#Methods

Swift- Methods are functions which are associates with particular type. In Swift, we define methods as follow:

struct Vehicle {
  //declare method without parameter and return type
  func registration()

  //declare method with paramter but no return type
  func topSpeed(gear: Int)

  //declare method with two parameters and return type
  func typeOfVehicle(tyres: Int, number: String) -> [String]
  
  //declare method with default parameter
  func topSpeed(_ speed: Int = 30)
  //method implementation
  func typeOfVehicle(tyres: Int, number: String) -> [String] {
    return []
  }
}

//calling method
let vehicle = Vehicle()
var type = vehicle.typeOfVehicle(tyres: 4, number: "90 BV 21")

Objective C- In Objective C, we can define methods as follow:

//declare method without parameters and return type
-(void)registration;
//declare method with parameter but no return type
-(void)topSpeed:(NSNumber *)gear; 
//declare method with two parameters and return type
-(NSArray *)typeOfVehicle: (NSNumber *)tyres (NSString *)number; 
//method implementation
-(NSArray *)typeOfVehicle: (NSNumber *)tyres (NSString *)number {
  return[];
}

//calling method
NSArray *result = [typeOfVehicle:@4 category:@"90 BV 21"];

#Enumeration

Swift- You can define enum with the enum keyword. The values inside enum are enumeration cases.

enum Direction {
  case north
  case south
  case east
  case west
}

let whereToGo = Direction.north

Objective C-Enums in Objective C is defined by following syntax:

typedef NS_ENUM(NSInteger, Direction) {
 North,
 South,
 East, 
 West
};