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Learning Exercise
Arrays are one of Swift's three primary collection types. Arrays are ordered lists of elements where the elements can be of any type, however, all elements of any given list must have the same type.
Arrays literals are written as a series of elements, each separated by commas, enclosed in square brackets. Empty arrays are just a pair of square brackets. Type names for arrays are written in one of two ways: Array<T> or [T] where T is the type of the elements in the array. When creating an empty array, the type must be specified.
let evenInts: Array<Int> = [2, 4, 6, 8, 10, 12]
var oddInts: [Int] = [1, 3, 5, 7, 9, 11, 13]
let greetings = ["Hello!", "Hi!", "¡Hola!"]
var myStringArray: [String] = []
Elements of an array can be accessed individually by supplying the index of the element inside square brackets following the array; array indices are Ints and start with 0 for the first (leftmost) element. This subscript notation can be used to get the element at that index as well as to set the element at that index, provided the array was defined as a variable (i.e. using var).
Trying to access elements at indices outside the valid range of indices will result in a runtime error that crashes the program. Since any invalid array index access will crash a program, it is common to test arrays to see if they are empty before working with them by checking the isEmpty property or checking if an index is valid by ensuring that it is greater than or equal to 0 and less than the array's count property.
evenInts[2]
// => 6
oddInts[0] = 27
// oddInts is now [27, 3, 5, 7, 9, 11, 13]
// these operations are not allowed
greetings[3]
// error: Execution was interrupted, reason: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0).
evenInts[1] = 0
// Cannot assign through subscript: 'evenInts' is a 'let' constant
The elements of an array can be stepped through one at a time using a for-in loop. This type of loop takes each element of the array, in order, and binds the element to a specified name for further processing inside the loop body. For example, to print out all of the odd integers in an array one can write:
let ints = [1, 3, 6, 14, 17, 8, 23, 5, 18, 11]
for int in ints {
if !int.isMultiple(of: 2) {
print(int)
}
}
// prints out:
// 1
// 3
// 17
// 23
// 5
// 11
As a magician-to-be, Elyse needs to practice some basics. She has a stack of cards that she wants to manipulate.
To make things a bit easier she only uses the cards 1 to 10.
Implement the function getCard(at:from:) that returns the card at position index from the given stack.
let index = 2
getCard(at: index, from: [1, 2, 4, 1])
// => 4
Implement the function setCard(at:in:to) that returns a new stack that is a copy of the input stack but which has the card at position index changed to the new card provided. If the given index is not a valid index in the stack, the original stack should be returned, unchanged.
let index = 2
let newCard = 6
setCard(at: index, in: [1, 2, 4, 1], to: newCard)
// => [1, 2, 6, 1]
Implement the function insert(_:atTopOf:) that returns a copy of the stack with the new card provided added to the top of the stack.
let newCard = 8
insert(newCard, atTopOf: [5, 9, 7, 1])
// => [5, 9, 7, 1, 8]
Implement the function removeCard(at:from:) that returns a copy of the stack which has had the card at position index removed. If the given index is not a valid index in the stack, the original stack should be returned, unchanged.
let index = 2
removeCard(at: index, from: [3, 2, 6, 4, 8])
// => [3, 2, 4, 8]
Implement the function removeTopCard(_:) that returns a copy of the stack which has had the card at the top of the stack removed. If the given stack is empty, the original stack should be returned, unchanged.
removeTopCard([3, 2, 6, 4, 8])
// => [3, 2, 6, 4]
Implement the function insert(_:atBottomOf:) that returns a copy of the stack with the new card provided added to the bottom of the stack.
let newCard = 8
insert(newCard, atBottomOf: [5, 9, 7, 1])
// => [8, 5, 9, 7, 1]
Implement the function removeBottomCard(_:) that returns a copy of the stack which has had the card at the bottom of the stack removed. If the given stack is empty, the original stack should be returned, unchanged.
removeBottomCard([8, 5, 9, 7, 1])
// => [5, 9, 7, 1]
Implement the function checkSizeOfStack(_:_:) that checks whether the size of the stack is equal to a given stackSize or not.
let stackSize = 4
checkSizeOfStack([3, 2, 6, 4, 8], stackSize)
// => false
Implement the function evenCardCount(_:) that steps through the stack and counts the number of even cards in it.
evenCardCount([3,8,4,5,1,6,10])
// => 4
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