"Cgfloat Is Not Convertible to Int" When Trying to Calculate an Expression

CGFloat is not convertible to Int when trying to calculate an expression

You have already explained and solved the matter perfectly. It's simply a matter of you accepting your own excellent explanation:

It works perfectly fine if ... I just give it a literal value ... But when I go with any variable or constant or expression containing one, it displays an error "CGFloat is not convertible to Int".

Correct. Numeric literals can be automatically coerced to another type, such as CGFloat. But variables cannot; you must coerce them, explicitly. To do so, initialize a new number, of the correct type, based on the old number.

So, this works automagically:

let f1 : CGFloat = 1.0
let f2 = f1 + 1

But here, you have to coerce:

let f1 : CGFloat = 1.0
let f2 = 1
let f3 = f1 + CGFloat(f2)

It's a pain, but it keeps you honest, I guess. Personally I agree with your frustration, as my discussion here will show: Swift numerics and CGFloat (CGPoint, CGRect, etc.) It is hard to believe that a modern language is expected to work with such clumsy numeric handling, especially when we are forced against our will to bang into the Core Graphics CGFloat type so frequently in real-life Cocoa programming. But that, it seems, is the deal. I keep hoping that Swift will change in this regard, but it hasn't happened so far. And there is a legitimate counterargument that implicit coercion, which is what we were doing in Objective-C, is dangerous (and indeed, things like the coming of 64-bit have already exposed the danger).

UInt8 is not convertible to CGFloat error in iOS Swift

You have to do it explicitly as

var spacing:CGFloat = CGFloat((avatarContentcroll.frame.size.width) - CGFloat(columns) * (dimension))/(columns+1)
var scHeight:CGFloat = CGFloat(spacing + (CGFloat(numberOfAvatars)/CGFloat(columns)) * (dimension + spacing))

or you can try converting every expression in CGFloat

var spacing:CGFloat = ((avatarContentcroll.frame.size.width) - CGFloat(columns) * (dimension))/(columns+1)
var scHeight:CGFloat = spacing + (CGFloat(numberOfAvatars)/CGFloat(columns)) * (dimension + spacing)

'CGFloat' is not convertible to 'Double' error in Swift (iOS)

In swift there is no implicit conversion of numeric data types, and you are mixing integers and floats.
You have to explicitly convert the indexes to CGFloats:

var intWidth = ( CGFloat(i) * (sizeOfImage.width/3.0))
var fltHeight = ( CGFloat(j) * (sizeOfImage.height/3.0))

As often happening in swift, the error message is misleading - it says:

'CGFloat' is not convertible to 'Double'

whereas I'd expect:

'CGFloat' is not convertible to 'Int'

Understanding the rules for conversion in swift

4 is not a "value". It is a literal. So it can be interpreted however Swift likes. There is nothing to "convert"; it is used to create the value, but the created value will be a Float, because that is what you asked for.

But now try this:

let i : Int = 4
let mynum: Float = i

Ooooops.

To put it another way:

let mynum: Float = 4

is interpreted as

let mynum = Float(4) // we are _creating_ the value

But if we start with i, you have to create the value:

let i : Int = 4
let mynum: Float = Float(i)

Swift won't do that for you.

BONUS LESSON Hold my beer and watch this:

struct Dog : IntegerLiteralConvertible {
    var number : Int?
    init(integerLiteral: Int) {
        self.number = integerLiteral
    }
}
let dog : Dog = 42

Float works like that, sort of.

Float' is not convertible to 'UInt8' in Swift

The error message is misleading but the problem is that Swift doesn't do implicit type conversions — just to pull one part of your expression out:

r / n

r is a floating point type. n is an integer type. In C the promotion rules would implicitly concert n to a float. That doesn't happen in Swift.

You probably want explicitly to cast all your integer types to Float to resolve the issue.

Swift numerics and CGFloat (CGPoint, CGRect, etc.)

I wrote a library that handles operator overloading to allow interaction between Int, CGFloat and Double.

https://github.com/seivan/ScalarArithmetic

As of Beta 5, here's a list of things that you currently can't do with vanilla Swift.
https://github.com/seivan/ScalarArithmetic#sample

I suggest running the test suite with and without ScalarArithmetic just to see what's going on.

Swift Double is Not Convertible to CGFloat

Convert the values that need to be CGFloat to a CGFloat.

path.addArcWithCenter(center, radius: CGFloat(radius), startAngle: CGFloat(0.0), endAngle: CGFloat(M_PI) * 2.0, clockwise: true)

startAngle probably shouldn't need to be converted though if you're just passing a literal. Also note that this isn't a C style cast, but actually converting between different Swift Types.

Edit: Looking at your whole function, this works.

func drawCircle() {
        // Drawing code
        var bounds:CGRect = self.view.bounds
        var center = CGPoint()
        center.x = bounds.origin.x + bounds.size.width / 2.0
        center.y = bounds.origin.y + bounds.size.height / 2.0
        var radius = (min(bounds.size.width, bounds.size.height) / 2.0)
        var path:UIBezierPath = UIBezierPath()
        path.addArcWithCenter(center, radius: CGFloat(radius), startAngle: CGFloat(0.0), endAngle: CGFloat(Float(M_PI) * 2.0), clockwise: true)
        path.stroke()    
    }

how to convert Int32 value to CGFloat in swift?

To convert between numerical data types create a new instance of the target type, passing the source value as parameter. So to convert an Int32 to a CGFloat:

let int: Int32 = 10
let cgfloat = CGFloat(int)

In your case you can either do:

let width = CGFloat(CMVideoFormatDescriptionGetDimensions(device.activeFormat.formatDescription as CMVideoFormatDescriptionRef!).width)
let height = CGFloat(CMVideoFormatDescriptionGetDimensions(device.activeFormat.formatDescription as CMVideoFormatDescriptionRef!).height)

myLayer?.frame = CGRectMake(0, 0, width, height)

or:

let width = CMVideoFormatDescriptionGetDimensions(device.activeFormat.formatDescription as CMVideoFormatDescriptionRef!).width
let height = CMVideoFormatDescriptionGetDimensions(device.activeFormat.formatDescription as CMVideoFormatDescriptionRef!).height

myLayer?.frame = CGRectMake(0, 0, CGFloat(width), CGFloat(height))

Note that there is no implicit or explicit type casting between numeric types in swift, so you have to use the same pattern also for converting a Int to Int32 or to UInt etc.

Ambiguous without more context error in Swift

You seem to declare the function as accepting

(attribute: NSLayoutAttribute, offset: CGFloat)

But you pass

(attribute: NSLayoutAttribute, offset: int)

Try

[(NSLayoutAttribute.centerX, CGFloat(0)), (NSLayoutAttribute.centerY, CGFloat(30))]

Int is not directly convertible to float

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