Random number generating unique numbers in Objective-C?

Question

I want to generate random numbers between 1-100 in Objective-C. Each random number should be unique and not the same as a previously generated random number.

Check out the many other questions on this topic, e.g. http://stackoverflow.com/questions/160890/generating-random-numbers-in-objective-c — pmdj, Jun 17 '11 at 11:28
I came across this, and I thought I should share that you should prefer arc4random_uniform(X) to arc4random() % X — borrrden, Jul 27 '12 at 04:35

score 78 · Answer 1 · edited Feb 05 '18 at 23:43

Check this links

Generating Random Numbers in Objective-C

How do I generate random numbers on the iPhone?
```
int r = arc4random() % 100;
```

Objective-C: Get random number

-(int)getRandomNumberBetween:(int)from and:(int)to {

    return (int)from + arc4random() % (to-from+1);
}

How to use:

1) Implement method above into your .m file

2) Add the following line to your .h file:

-(int)getRandomNumberBetween:(int)from and:(int)to;

3) Call the method like:

int randomNumber = [self getRandomNumberBetween:9 and:99];
//this gets you a random number between 9 and 99

Random Numbers in Objective-C

score 6 · Accepted Answer · edited Aug 23 '12 at 12:30

6

arc4random() %(100)-1 this is worked for me.

edited Aug 23 '12 at 12:30

Suresh Varma

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answered Jun 17 '11 at 11:34

Tirth

7,801
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3

From `man arc4random`: *arc4random_uniform() will return a uniformly distributed random number less than upper_bound. arc4random_uniform() is recommended over constructions like ``arc4random() % upper_bound'' as it avoids "modulo bias" when the upper bound is not a power of two.* – Manav Sep 11 '12 at 07:45
also, note that the upper bound in `u_int32_t arc4random_uniform(u_int32_t upper_bound)` is not inclusive, i.e. `arc4random_uniform(1)` will always give you zeroes. – Manav Sep 11 '12 at 07:58

score 5 · Answer 3 · answered Jun 17 '11 at 11:28

5

Use arc4random and store the results in an NSSet which will take care of the duplicates for you.

answered Jun 17 '11 at 11:28

Abizern

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score 4 · Answer 4 · answered Jan 22 '15 at 13:02

An other easy way is to do this is the use the arc4random_uniform() method:

Calling arc4random_uniform(N) return a random number from 0 to N-1. To get a number from 1 to N, you can use:

NSUInteger r = arc4random_uniform(N) + 1;

where N is the max number that you are looking for. In Swift, you can do it as:

var randomIndex:UInt32 = arc4random_uniform(N) + 1

e.g. if you want to get a random number between 1 and 100, just call as:

NSUInteger r = arc4random_uniform(100) + 1;

or in swift:

var randomIndex:UInt32 = arc4random_uniform(100)+1

score 2 · Answer 5 · edited Dec 05 '13 at 19:20

This is the code which generate unique random numbers...

-(void)UniqueRandom{

    int T[11];
    BOOL flag;
    for(int i=0;i<10;i++){

        int ranNo=  random()%100+1;
        flag=TRUE;
        int s=(sizeof T); 

        for(int x=0;x<s;x++){

            if(ranNo==T[x]){
                i--;
                flag= FALSE;
                break;
            }
        }

        if(flag) T[i]=ranNo;
    }

    for(int j=0;j<100;j++)  NSLog(@"unique random %d",T[j]);
    }
}

Happy coding..

score 1 · Answer 6 · answered Nov 22 '14 at 18:10

This method will generate array of unique random number in the interval of high and low range.

-(void)generateRandomUniqueNumberInRange :(int)rangeLow :(int)rangeHigh{
    NSMutableArray *unqArray=[[NSMutableArray alloc] init];
    int randNum = arc4random() % (rangeHigh-rangeLow+1) + rangeLow;
    int counter=0;
    while (counter<rangeHigh-rangeLow) {
        if (![unqArray containsObject:[NSNumber numberWithInt:randNum]]) {
            [unqArray addObject:[NSNumber numberWithInt:randNum]];
            counter++;
        }else{
            randNum = arc4random() % (rangeHigh-rangeLow+1) + rangeLow;
        }

    }
    NSLog(@"UNIQUE ARRAY %@",unqArray);

}

Random number generating unique numbers in Objective-C?

6 Answers6