rand() in decimals.

This is a discussion on rand() in decimals. within the C++ Programming forums, part of the General Programming Boards category; Hi, I'm wondering how do I generate random numbers in decimals? Meaning between 0-1. Any ideas? rand() returns from the ...

  1. #1
    Registered User
    Join Date
    Mar 2005
    Posts
    54

    rand() in decimals.

    Hi, I'm wondering how do I generate random numbers in decimals?
    Meaning between 0-1.

    Any ideas? rand() returns from the minimum of 1.

  2. #2
    C++ Witch laserlight's Avatar
    Join Date
    Oct 2003
    Location
    Singapore
    Posts
    23,629
    Read Prelude's article on Using rand(), in particular about creating a uniform deviate.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  3. #3
    Registered User
    Join Date
    Mar 2005
    Posts
    54
    Thanks for the link, my mind must've slipped as this could also be done.

    Code:
           float k = (rand()%10);
           k = k/10;

  4. #4
    Code Goddess Prelude's Avatar
    Join Date
    Sep 2001
    Posts
    9,855
    >float k = (rand()%10);
    >k = k/10;
    Apparently you didn't read the entire article. :P
    My best code is written with the delete key.

  5. #5
    Unregistered User Yarin's Avatar
    Join Date
    Jul 2007
    Posts
    1,896
    I've always done it like so:
    Code:
    float frand(int chop, int perk = 10) {
       return (float(rand() % chop) * pow(10.0, float(perk))) / pow(10.0, float(perk));   }
    A class that doesn't overload all operators just isn't finished yet. -- SmugCeePlusPlusWeenie
    A year spent in artificial intelligence is enough to make one believe in God. -- Alan J. Perlis

  6. #6
    Kernel hacker
    Join Date
    Jul 2007
    Location
    Farncombe, Surrey, England
    Posts
    15,677
    Quote Originally Posted by Yarin View Post
    I've always done it like so:
    Code:
    float frand(int chop, int perk = 10) {
       return (float(rand() % chop) * pow(10.0, float(perk))) / pow(10.0, float(perk));   }
    You probably want to read (and understand) Prelude's page too - that is, if you care about the distribution of your random numbers. [And if you REALLY want good random numbers, don't use rand - as it's by no means guaranteed to be "good"].

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  7. #7
    Unregistered User Yarin's Avatar
    Join Date
    Jul 2007
    Posts
    1,896
    I did read it quite a while ago, but I figured out that rand() was producing pretty much the same thing as her version of rand(). All I have to do is call srand() every 1k calls to rand().
    A class that doesn't overload all operators just isn't finished yet. -- SmugCeePlusPlusWeenie
    A year spent in artificial intelligence is enough to make one believe in God. -- Alan J. Perlis

  8. #8
    Kernel hacker
    Join Date
    Jul 2007
    Location
    Farncombe, Surrey, England
    Posts
    15,677
    Quote Originally Posted by Yarin View Post
    I did read it quite a while ago, but I figured out that rand() was producing pretty much the same thing as her version of rand(). All I have to do is call srand() every 1k calls to rand().
    Calling srand again after calling it the first time will NOT improve the distribution of your sequence - it will restart the sequence with a different seed, and depending on the seed value, it may give you the same sequence as last time or a different sequence. But it won't make the distribution any better.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

Popular pages Recent additions subscribe to a feed

Similar Threads

  1. Need help to show decimals
    By engstudent363 in forum C Programming
    Replies: 4
    Last Post: 02-19-2008, 03:13 PM
  2. allow decimals
    By dankassdann in forum C++ Programming
    Replies: 3
    Last Post: 10-28-2006, 06:41 PM
  3. multiple decimals = problem
    By Unregistered in forum C Programming
    Replies: 4
    Last Post: 07-18-2002, 08:32 AM
  4. Decimals To Binary
    By kas2002 in forum C++ Programming
    Replies: 8
    Last Post: 06-08-2002, 11:12 AM
  5. Decimals to Fractions
    By ToasterPas in forum C++ Programming
    Replies: 4
    Last Post: 12-28-2001, 11:58 AM

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21