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Swift Random Numbers: arc4random
Random. Our world is full of chance. One day a person wears a red shirt. Then green, blue, white. Our choice is random—in Swift we compute random Ints with a Foundation function.
With arc4random, we can begin a random sequence of numbers. Our program will begin a different sequence each time it is executed.
A first example. This example uses the arc4random function. In Xcode you can scroll through a list of functions by typing a few characters like "ar."
Arc4random: This returns a random number. As we see in the output this number has a large range but is positive.
Here: We use some logic in a repeat-while loop to test our random numbers. We use modulo division to terminate the loop.
RepeatSwift program that uses arc4random
import Foundation
// Use infinite "repeat while true" loop.
repeat {
// Get random number with arc4random.
let number = arc4random()
print("The computer selected: \(number)")
// Check for multiple of 10.
if number % 10 == 0 {
print("Divisible by 10, stopping loop.")
break
}
if number % 5 == 0 {
print("Divisible by 5, you are a winner.")
}
} while true
Output
The computer selected: 1580707251
The computer selected: 2169372518
The computer selected: 2188614733
The computer selected: 2102187726
The computer selected: 1259434845
Divisible by 5, you are a winner.
The computer selected: 4203979483
The computer selected: 3751678511
The computer selected: 1143995553
The computer selected: 1399438296
The computer selected: 4189143210
Divisible by 10, stopping loop.
Arc4random, seed. With arc4random, a different sequence is generated each time a program is run. No special seed value must be specified.
Important: With arc4random, programs will not have the same results each time they are run.
Swift program that shows random numbers
import Foundation
// With arc4random we do not need to seed the random number generator.
// ... A difference sequence is generated each time.
print("Test")
for i in 0...3 {
print(arc4random())
}
Output
Test
2350561563
3189423288
1041162380
2422311100
(Second run)
Test
1179004133
1484905321
2378084349
2120303966
With helpful Foundation methods, we generate random numbers in Swift. Arc4random is used for best pseudo-random results. It does not need a special seed.
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