TTS Swift Notes: Strings & Characters

Question 1

What is a string literal?

Answer 1

A fixed sequence of textual character surrounded by a pair of double quotes (“”).

Question 2

When do you use a string literal?

Answer 2

As an initial value for a constant or variable.

let someString = “Some string literal value”

Question 3

How do you create an empty String?

Answer 3

Either assign an empty string literal to a variable or initialize a new String instance with initializer syntax.

• var emptyString = “” // empty string literal
• var anotherEmptyString = String() // initializer syntax
• // these two strings are both empty, and are equivalent to each other

Question 4

What method checks a String’s Boolean to find out if it is empty?

Answer 4

.isEmpty

Question 5

How do you indicate whether a particular String can be modified (or mutated)?

Answer 5

Assign it to a variable (in which case it can be modified) or to a constant (in which case it cannot be modified).

1. var variableString = “Horse”
2. variableString += “ and carriage”
3. // variableString is now “Horse and carriage”
4. let constantString = “Highlander”
5. constantString += “ and another Highlander”

// this reports a compile-time error - a constant string cannot be modified

Question 6

How do you access the individual character values for a string?

Answer 6

By iterating over its characters property with a for-in loop

1. for character in "Dog!🐶".characters {
2. print(character)
3. }
4. // D
5. // o
6. // g
7. // !
8. // 🐶

Question 7

You can add to a string value with what two operators?

Answer 7

1. Addition operator (+)

2. Assignment operator (+=)

Question 8

What method can add a value to a string variable?

Answer 8

.append

Question 9

String interpolation is a way to do what?

Answer 9

To construct a new String value from a mix of constants, variables, literals, and expressions by including their values inside a string literal.

Question 10

What is unicode?

Answer 10

An international standard for encoding, representing, and processing text in different writing systems.

Question 11

What does unicode allow you to do?

Answer 11

To represent almost any character from any language in a standardized form, and to read and write those characters to and from an external source such as a text file or web page.

Question 12

What is a unicode scalar?

Answer 12

A unique 21-bit number for a character or modifier, such as U+0061 for LATIN SMALL LETTER A(“a”).

Question 13

What is the Unicode scalar range?

Answer 13

U+0000 to U+D7FF inclusive OR U+E000 to U+10FFFF inclusive.

Question 14

What is an extended grapheme cluster?

Answer 14

A sequence of one or more Unicode scalars that (when combined) produce a single human-readable character. They area a flexible way to represent many complex script characters as a single Character value. EX: é

Question 15

What method/property retrieves the count of the Character values in a string?

Answer 15

.count

Question 16

Calling String.Index() does what?

Answer 16

Corresponds to the position of each Character in the string.

Question 17

Can Swift string be indexed by integer values?

Answer 17

No

Question 18

What property should you use to access the first position Character of a String?

Answer 18

startIndex

Question 19

The endIndex property is what position of a String?

Answer 19

After the String’s last character.

Question 20

If a String is empty, startIndex and endIndex are what?

Answer 20

Equal

Question 21

Any index in a String can be accessed from any other index by chaining the predecessor(), successor() or this method.

Answer 21

advancedBy(_:)

Question 22

What method allows a String.Index value to access its immediately preceding index?

Answer 22

predecessor()

Question 23

What method allows a String.Index value to access its immediately succeeding index?

Answer 23

successor()

Question 24

What method inserts a character into a string at a specified index?

Answer 24

insert(_:atIndex:)

Question 25

What method inserts the contents of another string at a specified index?

Answer 25

insertContentsOf(_:at:)

Question 26

What method removes a character from a string at a specified index?

Answer 26

removeAtIndex(_:)

Question 27

What method removes a substring at a specified range?

Answer 27

removeRange(_:)

Question 28

What are the three ways that Swift provides to compare textual values?

Answer 28

1. string and character equality
   
   2. prefix equality
   3. suffix equality

Question 29

What two operators check string and character equality?

Answer 29

The equal to operator (==)

The not equal to operator (!=)

Question 30

In Swift, are string and character comparisons locale-sensitive?

Answer 30

No

Question 31

What method checks if a string has a particular string prefix?

Answer 31

hasPrefix(_:)

Question 32

What method checks if a string has a particular string suffix?

Answer 32

hasSuffix(_:)

Question 33

hasPrefix(:) and hasSuffix(:) return what kind of value?

Answer 33

Boolean

Question 34

Encoding forms encode strings into small chunks called what?

Answer 34

Code units

Question 35

UTF-8 encoding form has how many code units?

Answer 35

8-bit code units.

Question 36

You can access a UTF-8 representation of a String by iterating over its what?

Answer 36

utf8 property

Question 37

The utf8 property is of what type?

Answer 37

String.UTF8View

Question 38

How do you access a Unicode scalar representation of a String value?

Answer 38

By iterating over its unicodeScalars property.

Question 39

The unicodeScalars property is of what type?

Answer 39

UnicodeScalarView

Question 40

UnicodeScalarView is a collection of what value type?

Answer 40

UnicodeScalar

Question 41

Each UnicodeScalar value can be used to do what?

Answer 41

Construct a new String value.