[2 days left] Whatâ€™s wrong with your cloud strategy? Learn why multicloud solutions matter with Nimble Storage.Register Now

x
Solved

# Generating different sequences of random numbers

Posted on 2000-02-15
Medium Priority
284 Views
When I use randomize() and rand(), I get a sequence of random numbers in the range I need. However, I need to generate about a 1000 DIFFERENT sequences of random numbers in the given range. About 500 or so runs result in 500 same sequences since randomize() uses the system clock as a seed and 500 runs take less than a second to execute. In other words, since my program runs faster than the seed (clock seconds) can change, I get a lot of same sequences of random numbers. I tried slowing down the program by inserting loops but then it runs too slow. Is there anyway to get a 1000 different sequences?
0
Question by:mrmind3
[X]
###### Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

• Help others & share knowledge
• Earn cash & points

LVL 22

Expert Comment

ID: 2524814
On a windows computer you could use GetTickCount as a seed.

Are you seeding the randome number more than once per run of the program?  it sounds like you are.  There is no need.  Just seed 1 time, when the program starts and you won't get any repeats.
0

Author Comment

ID: 2524898
But I do need to seed several times. I need to get  about a 1000 DIFFERENT sequences of random numbers not just one sequence.
0

LVL 1

Expert Comment

ID: 2525048
You could XOR all the generated random numbers, and use this as the next seed.
And perform some bit-swapping, or whatever, depending if the number is odd or even or so. This will for sure make 1000 different random sequences.
0

LVL 84

Expert Comment

ID: 2525087
randomize() once
then get 1000 different sequences of rand()
0

LVL 1

Expert Comment

ID: 2525098
This is what nietod also proposed, but mrmind3 wants to be able to start every sequence with a new seed.
0

LVL 22

Accepted Solution

nietod earned 200 total points
ID: 2525116
>> But I do need to seed several times.
>> I need to get  about a 1000 DIFFERENT
>> sequences of random
>> numbers not just one sequence.
what is?

2 5 2 1 7 9 3 4

Is that a sequence of 8 random numbers?  Arre you sure it is not two sequences of 4 random numbers?  Perhaps it is 4 sequences of 2 random numbers

Just seed once, then generate the random numbers.  Where a sequence ends and another begins is arbitrary.  That is, it is up to you.  you don't have to use randomize() to start each sequence, just to start the process.
0

LVL 1

Expert Comment

ID: 2525129
I agree, but the second sequence of 4 numbers is affected by the first sequence, coz the rand() function is implemented in the way it has memory over the last generated numbers.
0

LVL 22

Expert Comment

ID: 2525283
If you want to be technical about it the numbers aren't random in either case.  But in either case the numbers will be evenly disrtibuted over the integer range and will display any easily detectable pattern.  So there is no difference in either case.  They are equally "random"
0

## Featured Post

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Errors will happen. It is a fact of life for the programmer. How and when errors are detected have a great impact on quality and cost of a product. It is better to detect errors at compile time, when possible and practical. Errors that make their waâ€¦
What is C++ STL?: STL stands for Standard Template Library and is a part of standard C++ libraries. It contains many useful data structures (containers) and algorithms, which can spare you a lot of the time. Today we will look at the STL Vector. â€¦
The viewer will learn how to use the return statement in functions in C++. The video will also teach the user how to pass data to a function and have the function return data back for further processing.
The viewer will learn how to clear a vector as well as how to detect empty vectors in C++.
###### Suggested Courses
Course of the Month14 days, 1 hour left to enroll