Better way of using arc4random - ios

Question

I have a random method to create 2 random integers. My concern is that %65-%70 of outputs are same integers like "5-5" "4-4" "3-3".
-(void)random{
NSUInteger randomNumber = arc4random_uniform(5);
switch (randomNumber) {
case 0:
_tile2.image = [UIImage imageNamed:#"one.png"];
break;
case 1:
_tile2.image = [UIImage imageNamed:#"two.png"];
break;
case 2:
_tile2.image = [UIImage imageNamed:#"three.png"];
break;
case 3:
_tile2.image = [UIImage imageNamed:#"four.png"];
break;
case 4:
_tile2.image = [UIImage imageNamed:#"five.png"];
break;
}
NSUInteger randomNumber2 = arc4random_uniform(5);
switch (randomNumber2) {
case 0:
_tile3.image = [UIImage imageNamed:#"one.png"];
break;
case 1:
_tile3.image = [UIImage imageNamed:#"two.png"];
break;
case 2:
_tile3.image = [UIImage imageNamed:#"three.png"];
break;
case 3:
_tile3.image = [UIImage imageNamed:#"four.png"];
break;
case 4:
_tile3.image = [UIImage imageNamed:#"five.png"];
break;
}
}
Should i create 25 different case to reach better result?
NSUInteger randomNumber = arc4random_uniform(25);
switch (randomNumber) {
case 0:
_tile2.image = [UIImage imageNamed:#"one.png"];
_tile3.image = [UIImage imageNamed:#"one.png"];
break;
case 1:
_tile2.image = [UIImage imageNamed:#"one.png"];
_tile3.image = [UIImage imageNamed:#"two.png"];
break;
case 2:
_tile2.image = [UIImage imageNamed:#"one.png"];
_tile3.image = [UIImage imageNamed:#"three.png"];
break;
case 3:
_tile2.image = [UIImage imageNamed:#"one.png"];
_tile3.image = [UIImage imageNamed:#"four.png"];
break;
case 4:
_tile2.image = [UIImage imageNamed:#"one.png"];
_tile3.image = [UIImage imageNamed:#"five.png"];
break;
case 5:
_tile2.image = [UIImage imageNamed:#"two.png"];
_tile3.image = [UIImage imageNamed:#"one.png"];
break;
...
}
}
arc4random_uniform is great for getting one random integer. When i need to get 2 or more random numbers, the outputs are not that great. What is the best way of doing this?

Answer 1

Sorry, but I don't believe you. You must be doing something other than what you've shown. The following code pasted into Playground consistently gives around a 20% match, not the 65-70% you claim:
import Cocoa
let sampleSize = 1000
var count = 0
for i in 1...sampleSize {
var randomNumber1 = arc4random_uniform(5)
var randomNumber2 = arc4random_uniform(5)
if randomNumber1 == randomNumber2 {
++count
}
}
println( Double(count) / Double(sampleSize) )
Whatever problem you're having, it isn't with how arc4random_uniform generates pairs of values.

Answer 2

Would using an array of numbers be a solution for you?
You can have a mutable array of numbers `[#0, #1, #2, #3, #4] and retrieve one number from a random index
NSMutableArray *array = [NSMutableArray arrayWithObjects:#0, #1, #2, #3, #4];
NSInteger firstIndex = arc4random_uniform([array count]);
NSNumber *firstNumber = array[index];
Remove the number you've just found:
[array removeObjectAtIndex:firstIndex];
And than repeat the same for the second number. The first retrieved number won't be in the array anymore so even if the arc4random_uniform() gives you the same value (your 65-70% case) the actual number you are gonna use in your switch case it's gonna be different.
This approach is probably a bit clumsy, but I think it does what you need giving you a bit of control over the randomness.