Control Flow

if / else if / else

Parentheses around the condition are not required. Braces { } are mandatory.

if temperature > 80 {
    print("Overheating")
} else {
    print("Normal temperature")
}

else if chains are fully supported and may be nested to any depth:

let score = 85

if score >= 90 {
    print("A")
} else if score >= 80 {
    print("B")
} else if score >= 70 {
    print("C")
} else {
    print("F")
}

while

Repeats the body as long as the condition is truthy.

let retries = 0
while retries < 5 {
    print("Attempting connection...")
    retries += 1
}

for / in

Iterates over every element of a List. The loop variable is scoped to the loop body.

let nodes = ["web-01", "web-02", "db-01"]
for node in nodes {
    print("Checking node: " + node)
}

Combined with range() for numeric iteration:

for i in range(5) {
    print("Step " + str(i))   // 0 1 2 3 4
}

for i in range(1, 6) {
    print(str(i))              // 1 2 3 4 5
}

break

Immediately exits the nearest enclosing while or for loop.

let i = 0
while i < 100 {
    i += 1
    if i > 10 {
        break     // stops the loop when i reaches 11
    }
}
print(i)   // 11

Use break inside a loop. The current interpreter does not consistently reject it outside loops; that behavior should not be relied on.

continue

Skips the rest of the current loop iteration and jumps to the next one.

for i in range(10) {
    if i % 2 == 0 {
        continue   // skip even numbers
    }
    print(i)       // prints 1, 3, 5, 7, 9
}

Use continue inside a loop. The current interpreter does not consistently reject it outside loops; that behavior should not be relied on.