Swift Live Reference

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

— Merlin, The Coder

Comments[edit]

Comments are used by humans to document code for other humans. They have no effect on the program itself.

In Swift, it is customary to capitalize all types.

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

Variables (named values which may change) use the var keyword

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

Conditionals are used to execute a segment of code based upon a condition being met.

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

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

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

for loops are 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 ten
for n in 1 ... 10 {
    print(n)
}

while loops are helpful when the condition may initially be false and the statements should not be executed.

while n < 10 {
    n += 1
}

repeat while loops are helpful when the statements should be executed at least once.

repeat {
    n += 1
} while n < 10