Generating a random negative NSInteger

Question

I'm trying to generate random negative NSInteger using the following code,

+ (NSInteger)getNegativeRandomNumber {
    uint32_t random = arc4random_uniform(2147483647); // where 2147483647 is the max 32-bit positive value returned by random function
    return (NSInteger)(-1 * random); // convert the positive into negative number
}

But occasionally this code gives me positive numbers. Do you see any issue with this code?

`return -(NSInteger)random;`. The issue is because of 64 bits and 32 bits architectures, and the `NSInteger` hasn't the same definition. And you are doing the `-` sutff, on the random, and the casting. — Larme, Mar 03 '17 at 10:50

score 2 · Answer 1 · answered Mar 03 '17 at 10:50

2

You get negative numbers with

return -(NSInteger)random;

You need first to cast to a signed type.

answered Mar 03 '17 at 10:50

vadian

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Probably would be good to explain why this is the case (i.e. negating an unsigned number will return an unsigned number so you need to convert to signed first). – Itai Ferber Mar 03 '17 at 16:19

Ravindra Shekhawat · Answer 2 · 2017-03-03T13:10:10.030

0

This will surely help....

-(int) generateRandomNumberWithlowerBound:(int)0
                               upperBound:(int) 2147483647
{
    int rndValue = lowerBound + arc4random() % (upperBound - lowerBound);
    return -(NSInteger)(rndValue);
}

edited Mar 03 '17 at 13:10

answered Mar 03 '17 at 10:54

Ravindra Shekhawat

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Generating a random negative NSInteger

2 Answers2