SpriteKit for loop - for-loop

Question

Hi I'm trying to follow a tutorial on Ray Wenderlich site
[http://www.raywenderlich.com/76740/make-game-like-space-invaders-sprite-kit-and-swift-tutorial-part-1][1]
so I'm going thru the functions breaking it down so i can get an understanding of how it works I've commented out stuff which i think i understand but this bit has me stumped
thanks for looking
the for loop whats the var row = 1 at the beginning doing ?
I've only ever done for lops like
for Position in 0...9
{
// do something with Position ten times
}
then whats the % in if row %3 mean?
for var row = 1; row <= kInvaderRowCount; row++ // start of loop
{
var invaderType: InvaderType // varible of atype etc
if row % 3 == 0
{
invaderType = .AType
} else if row % 3 == 1
hers the rest of the code
func makeInvaderOfType(invaderType: InvaderType) -> (SKNode) // function passes in a enum of atype,btype,ctype and returns sknode
{
var invaderColor: SKColor// variable for the colour
switch(invaderType)// switch statment if we pass in atype we will get red
{
case .AType:
invaderColor = SKColor.redColor()
case .BType:
invaderColor = SKColor.greenColor()
case .CType:
invaderColor = SKColor.blueColor()
default:
invaderColor = SKColor.blueColor()
}
let invader = SKSpriteNode(color: invaderColor, size: kInvaderSize)//variable of a skspritenode with color from switch statement size from vairiabe kinvadersize
invader.name = kInvaderName // name is invader fron let kinvadername
return invader //return the spritenode with color size name
}
func setupInvaders()
{
let baseOrigin = CGPoint(x:size.width/3, y:180) // vairible to hold cgpoint screen size /3 width 180 height
for var row = 1; row <= kInvaderRowCount; row++ // start of loop
{
var invaderType: InvaderType // varible of atype etc
if row % 3 == 0
{
invaderType = .AType
} else if row % 3 == 1
{
invaderType = .BType
} else
{
invaderType = .CType
}
let invaderPositionY = CGFloat(row) * (kInvaderSize.height * 2) + baseOrigin.y// varible to hold cgfloat row ? think its the incriment of the for loop times 16 times 2 = 32 plus 180 first time is 212 then 244
/* so if ive got his rightthe sum goes row = 1 kinvadersize.hieght *2 = 32 + baseoringin.y = 180
1 * 32 +180 = 212
2 * 32 + 180 = 392 but its 244
*/
println(row)
var invaderPosition = CGPoint(x:baseOrigin.x, y:invaderPositionY) // varible to hold cgpoint
println(invaderPosition.y)
for var col = 1; col <= kInvaderColCount; col++
{
var invader = makeInvaderOfType(invaderType)// varible that runs function and return the spritenode with color size name????
invader.position = invaderPosition
addChild(invader)
invaderPosition = CGPoint(x: invaderPosition.x + kInvaderSize.width + kInvaderGridSpacing.width, y: invaderPositionY)
}
}
}

Answer 1

If I understand your question correctly, here's the answer. Based on this code:
for var row = 1; row <= kInvaderRowCount; row++ // start of loop
{
var invaderType: InvaderType // varible of atype etc
if row % 3 == 0
{
invaderType = .AType
} else if row % 3 == 1
The first line means:
var row = 1: given a new variable, row, with a value of 1
row <= kInvaderRowCount: as long as the variable row is less than or equal to kInvaderRowCount, keep running the for loop
row++: after each time the loop is run, increment (increase) the value of row by 1
As for the "%", that is the modulo operator. It returns the remainder after a division operation on integer values. So if 7 divided by 3 = 2, with a remainder of 1, then
7 / 3 = 2
7 % 3 = 1
The modulus operator results in an integer. While 1 / 3 = 0.33..., 1 % 3 = 1. Because the remainder of 1 divided by 3 is 1.
1 % 3 = 1
2 % 3 = 2
3 % 3 = 0
4 % 3 = 1
5 % 3 = 2
6 % 3 = 0
see also: How Does Modulus Divison Work.