Random number in Objective-C [duplicate] - ios

Question

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Closed 11 years ago.
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Generating random numbers in Objective-C
iOS Random Numbers in a range
Generate non-repeating, no sequential numbers
I am looking for method that give me random numbers between two numbers, and the first number will be number that I choose between the numbers.
for example, if I give this random function 5 and 10 and 9 as the first number, so it will give me: 9,10,7,6,5,8
I tried to use it:
NSUInteger count = [array count];
for (NSUInteger i = 1; i < count; ++i) {
int nElements = count - i;
int n = (random() % nElements) + i;
while (n==`firstnumber`) {
n = (random() % nElements) + i;
}
}

Answer 1

int r = arc4random() % 9 + 5 will give you numbers between 5 and 13 including both of them.

Answer 2

the first number is set by me and the other numbers by the method ,and
every number is shown only one time
It looks like you are after a shuffling algorithm. The following category on NSMutableArray will do the job:
#interface NSMutableArray (Shuffling)
- (void)shuffle;
#end
#implementation NSMutableArray (Shuffling)
- (void)shuffle
{
// Fisher–Yates shuffle (modern algorithm)
// To shuffle an array a of n elements (indexes 0..n-1):
// for i from n − 1 downto 1 do
// j <-- random integer with 0 <= j <= i
// exchange a[j] and a[i]
// http://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle
for (int i = [self count] - 1; i >= 1; i--) {
int j = arc4random() % (i + 1);
[self exchangeObjectAtIndex:j withObjectAtIndex:i];
}
}
#end
Your requirement is that the number in the first position of the array is fixed (given by you). Then, you can do something like this:
Populate the array with all numbers between minValue and maxValue (both included) except for firstValue.
Shuffle the array.
Insert firstValue at the first position in the array.
Resulting in the following code:
NSInteger minValue = 5;
NSInteger maxValue = 10;
NSInteger firstValue = 9;
// minValue <= firstValue <= maxValue
// populate the array with all numbers between minValue
// and maxValue (both included) except for firstValue
NSMutableArray *ary = [NSMutableArray array];
for (int i = minValue; i < firstValue; i++) {
[ary addObject:[NSNumber numberWithInt:i]];
}
for (int i = firstValue + 1; i <= maxValue; i++) {
[ary addObject:[NSNumber numberWithInt:i]];
}
// --> (5,6,7,8,10)
// shuffle the array using the category method above
[ary shuffle];
// insert firstValue at the first position in the array
[ary insertObject:[NSNumber numberWithInt:firstValue] atIndex:0];
// --> (9,x,x,x,x,x)