Pdf is much better than png and jpeg for performance.

Optional

Whether a variable consists a value of nothing(nil). It saves memory and doesn’t memory until a value is assigned.

Cocoa touch class: Inherits from superclass.

dismiss when present is used. pop when push is used.

Label: Used when the text is of maximum 3 lines. Textview: Used when the text is in the form if a paragraph.

Aspect fill: Keep original size Scale to fill: to fit the entire screen

Optionals

we have to unwrap optionals to use them.

1. Force Unwrap: Not recommended

If the value of optional is nil, It will crash application.

var a: Int? = 5
var b: Int? = 3
//Using force unwrapping
var c = a! + b!
print(c)

Output

8