Swift Live Reference

Within these castle walls be forged Mavens of Computer Science ...

— Merlin, The Coder

Comments

Humans use comments to document code for other humans. They have no effect on the program's operation itself.

Single-line comments

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// single-line comments begin with two slashes

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Multi-line comments

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/* multi-line comments begin with slash-star and continue and continue until a closing star-slash */

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Output

print

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print("Hello, World!")

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print with separator

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print("to", "ease", "another's", "heartache", separator: "*")

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print with terminator

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print("to", "ease", "another's", "heartache", separator: "*", terminator: "<>") print("is", "to", "forget", "one's", "own", separator: "/")

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Types

In Swift, it is customary to capitalize all types.

Int

A signed integer value type

Float

A single-precision, floating-point value type

Double

A double-precision, floating-point value type

String

A Unicode string value that is a collection of characters

Constant and Variable Declarations

Constant declarations

Constants (named values that should never change) use the let keyword.

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let gravity = 9.81 // meters per second per second print(gravity)

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Variable Declarations

Variables (named values that could change) use the var keyword.

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var currentTemperature = 23.1 // degrees celsius print(currentTemperature)

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Control Structures

Control structures are used to alter the otherwise sequential flow of a program.

Conditionals

Conditionals are used to execute a segment of code if a condition is met.

if

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var n = 7 if n < 10 { print("n is less than 10") }

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else

if n < 10 {
    print("n is less than 10")
} else {
    print("n is not less than 10")
}

switch

switch n {
    case 0:
        print("n is zero")
    case 1:
        print("n is one")
    default:
        print("n is neither one nor zero")
}

Loops

Loops are used to repeat a segment of code until a condition is met.

for

The for loop is helpful when the number of iterations is known.

// From zero up to but excluding ten
for n in 0 ..< 10 {
    print(n)
}

// From one up to and including 10
for n in 1 ... 10 {
    print(n)
}

while

The while loop is helpful when the condition might initially be false and the statements should not be executed.

while n < 10 {
    n += 1
}

repeat while

The repeat while loop is helpful when the statements should be executed at least once.

repeat {
    n += 1
} while n < 10

References

• https://developer.apple.com/documentation/swift