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Swift Repeat While LoopUse the repeat-while loop to continue iterating until a condition is reached. Specify the break keyword.
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Repeat. Some things in Swift have no known endpoint—we stop them (break the loop) on demand. For a simple loop, we can invoke the "repeat" keyword.
Two keywords. The repeat loop requires a "repeat" and a "while" keyword. To have an infinitely repeating loop, we can use a "while true" part at the end.
First example. Here we have a repeat-while loop. We have a local variable named "i" and we increment this in the body of the repeat-while loop.
Note The loop ends when our variable reaches the value 6. We print the statement "I have N cats" on each iteration.
Swift program that uses repeat loop
var i = 0 // Use repeat loop. // ... No initial condition is checked. repeat { print("I have \(i) cats.") i += 1 } while i < 5
I have 0 cats. I have 1 cats. I have 2 cats. I have 3 cats. I have 4 cats.
Repeat, random numbers. Here is a simple program that repeats a function call. It terminates the repeat-while loop only when the function call returns a specific number.
Rand This returns a random number. In the following if-statement, we break if the number is even (not odd).
Random
True Consider using a "while-true" loop when an infinite (or indeterminate) loop is needed. A break can stop the loop.
Swift program that uses repeat loop, random numbers
import Foundation // Initialize a seed number. sranddev() // Get random number in repeat loop. // ... Print number. // If number is even then break the loop. repeat { let number = arc4random() print(number) // Check for even number. if number % 2 == 0 { print("Even number, stopping loop.") break } } while true
546090829 4220801392 Even number, stopping loop.
Repeat, example 3. The repeat-while loop does not check its condition before the loop body is entered. So a variable (like "x" in this program) can have any value.
Swift program that shows no initial check, repeat-while
var x = 999 repeat { // This block is entered on any value of x. // ... The value is not checked before the block is executed. print(x) } while x < 10
999
A summary. The repeat-while loop is the same as a "do-while" loop in C-like languages. The word "repeat" may be easier to read for programmers. Its while part is required.
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