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Getting a Random Number

Posted on July 22, 2009 by John Muchow in C

If you need to generate a random number within your iPhone application, you have to push aside Objective-C, as there is not a class with a method for generating random numbers (as in Java). The alternative is to use C, among the functions available are: rand(), srand(), random(), srandom() and arc4random().

arc4random() tends to be preferred as it does not require seeding, the function automatically initializes itself.

// Get random value between 0 and 99
int x = arc4random() % 100;
 
// Get random number between 500 and 1000
int y =  (arc4random() % 501) + 500);

Comments

2 Responses to “Getting a Random Number”

Alex says:

July 22, 2009 at 11:25 am

The freely available, and BSD licensed, Mersenne twister also works quite handsomely on the iPhone.
slimemoldjuice says:

July 22, 2009 at 6:28 pm

I tend to make a macro to do this:

#define RANDOM_INT(__MIN__, __MAX__) ((__MIN__) + arc4random() % ((__MAX__+1) – (__MIN__)))

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