How many lines of code can you program in hour?
A new campaign in the US that is spreading around internet is called “Hour of Code”, with a great video ad with celebrities and folks of all ages learning to code, and Obama giving a little encouragement.
I checked out HourofCode.org to see what it was all about. While a big chunk of the campaign is to get schools to teach programming, the thing I was interested in was the learning section. I decided to do one: program a game that could be used on iOS, through Make Games With Us.
The program is written in Objective-C, which I have never done before. So, some things I learned (or think I learned!) about programming a game for iOS / using Objective C:
- something.h means a class. To import it, include #import something.h. Not sure what the significance of the # is. You can import pre-existing classes.
- Syntax: Objective C uses { } to open and close things, and ; at the end of lines. [ ] seem to be important (even used when they are not an argument for something, just around the whole line). Seems to have to do with making something execute.
- To structure a program so it can rub:
@implementation NameOfClassBeingUsedAsScene (I believe)
-(id) init
{
if ((self = [super init])) // this is code to check things have been initialized properly, always include it in your init method
{
// program code goes here
} // end of the if(self=[super init]
// don’t put any extra code after the if – not sure if this is just for the program-a-game exercise, or if this is all the time. If all the time, effectively means the program is one big if.
return self;
} // end of the program, the -(id) init. after returns Self.
// can insert new methods below (i.e. outside) the program, but before the implementation ends.
@end // finishes the implementation
- You can import classes before the -(id) init. You can also create class level variables before the -(id) init.
- Objective C distinguishes between primitives and objects. You must(?) declare what a variable is: a primitive or an object. Primitives include int, float, bool, etc…)
- To declare a primitive:
type NAME (e.g. int Counter).
- To declare a new object of a class X, must use a *
class * NameOfNewObject;
Can also have it be:
class * NameOfNewObject= [[class alloc] init]
Not sure if the alloc is standard across all classes. As far as I can figure, this it the command that declares a new object of a class using whatever procedure that class uses to create a new object of that class (e.g. could randomize characteristics). It appears that it is not necessary to use a method to create an object. Edit: Yes, before you use the object, you need to initialize it. It appears that for the game program, Alloc is what does the initializing. However, not clear if that is standard.
- Objective C borrows terms from the movies: a screen is called a scene, and the Director is a tool that can be used to do certain things.
- You can use the term “self” to refer to the current scene (possibly?)
- To add an object to the current scene: [self addChild:NameOfObject]
- “++” increases a variable by 1
-
From the MakeAGameWithUs tutorial:
Basic Syntax
Objective-C syntax for declaring and calling methods is what makes it look the most different from languages like C++ and Java. The good news is that once you learn how it’s done the Objective-C way it will become clear that these languages follow the same basic principles.
To call a method: [ObjectName methodName]; For example:[hero shoot]; To call a method and pass a parameter:[ObjectName methodName: parameter]; For example:[self addChild: hero];
A base control later is CCLayer.
Method Syntax
Method Syntax
To declare a method in Objective-C, follow the following format:
-(type I return) nameOfMethod:
(type of first parameter) firstParameter
continuationOfMethodName:
(type of second parameter) secondParameterFor example, to declare a method that does not return anything and does not accept any parameters:
-(void) doSomething
{
NSLog(@"Hello World!");
}Or, to declare a method that returns an int and accepts a string:
-(int) doSomethingWithAString: (NSString*) myString
{
//returns the length of the string times ten
return [myString length] * 10;
}Or, to declare a method that returns an array and accepts multiple strings:
-(NSArray *) addThisStringToAnArray: (NSString*) firstString
andThisString: (NSString*) secondString
andAlsoThisString: (NSString*) thirdString
{
return [NSArray arrayWithObjects: firstString,
secondString,
thirdString, nil];
}- For your game to be dynamic and interactive, it needs to update frequently. Programs do this using a concept called frames, during every frame the entire screen is redrawn, and frames happen 60 times each second!
- To switch to a different screen (ie. scene), use “replaceScene”), which is called from the CCDirector.
[[CCDirector sharedDirector] replaceScene: [[NewScene] alloc] init]]
Those are my class notes 🙂 The final code for the project is below. 38 lines of code done, a little over an hour (incl writing this post).
—–
#import “GameplayLayer.h”
#import “Ship.h”
#import “MainCharacter.h”
#import “GameOverLayer.h”
int screenHeight;
int screenWidth;
MainCharacter * hero;
@implementation GameplayLayer
// the code inside the brackets after “-(id) init” is the code that runs once when you run your program. It is the very first thing to run.
-(id) init
{
if ((self = [super init])) // this is code to check things have been initialized properly, always include it in your init method
{
screenHeight = [[CCDirector sharedDirector] screenSize].height;
screenWidth = [[CCDirector sharedDirector] screenSize].width;
//initialize a ship
Ship * ship1 = [[Ship alloc] init];
//add the ship to the scene
[self addChild: ship1];
//increment the game’s number of enemies counter. I assume this is already declared in Gameplaylayer
numEnemies++;
// place the ship
ship1.position = ccp(screenWidth/2, screenHeight/2);
Ship * ship2 = [[Ship alloc] init];
[self addChild: ship2];
numEnemies++;
ship2.position = ccp(screenWidth/3, screenHeight/3);
Ship * ship3 = [[Ship alloc] init];
[self addChild: ship3];
numEnemies++;
ship3.position = ccp(screenWidth/4, screenHeight/4);
Ship * ship4 = [[Ship alloc] init];
[self addChild: ship4];
numEnemies++;
ship4.position = ccp(screenWidth/5, screenHeight/5);
Ship * ship5 = [[Ship alloc] init];
[self addChild: ship5];
numEnemies++;
ship5.position = ccp(screenWidth/6, screenHeight/6);
hero = [[MainCharacter alloc] init];
[self addChild: hero];
hero.position = ccp(screenWidth/2, screenHeight/10);
[self scheduleUpdate];
}
// don’t put any more code here
return self;
}
// put new methods here
-(void) update: (ccTime) dt
{
//this will get called every frame
//but only if the line [self scheduleUpdate] is in the init method
//gets the input object that stores all
//touches that happened this frame
KKInput * input = [KKInput sharedInput];
//get the position of the touch that began this frame
CGPoint touchPosition = [input locationOfAnyTouchInPhase:KKTouchPhaseBegan]; //returns (0.0,0.0) if no touch Position
if(touchPosition.x != 0.0 || touchPosition.y != 0.0)
{
[hero shootAt: ccp(screenWidth/2, screenHeight)];
}
//check victory condition
if(numEnemies == 0)
{
[[CCDirector sharedDirector] replaceScene:
[[GameOverLayer alloc] initWithPlayerName: playerName]];
//we’ve set the variable playerName to be your name 🙂
}
}
@end
Discovering my makerself 