random()?

This is a discussion on random()? within the C++ Programming forums, part of the General Programming Boards category; can anyone explain me the usage of random function what does this line mean? radom() %10;...

  1. #1
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    random()?

    can anyone explain me the usage of random function

    what does this line mean?

    radom() %10;
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  2. #2
    and the hat of wrongness Salem's Avatar
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    Perhaps

    cout << random() % 10 << endl;

    Will get the message across if you run it a few times

  3. #3
    Code Monkey Davros's Avatar
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    random() returns a value between 0 & MAX_RAND (usually 2^31).

    Because % returns the reminder of a division, calling random() % 10 will return a number between 0 & 9 inclusive.
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    thx
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    Seven years? civix's Avatar
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    the %10 means that the output will be between 0 and 10..if it was %20, that would make a random number between 0 and 20...one million is the highest number that you can put behind the % (dont you just hate counting 0's?)...hope that helps

  6. #6
    End Of Line Hammer's Avatar
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    >the %10 means that the output will be between 0 and 10..
    Wrong, it's 0-9, as already stated.

    >one million is the highest number that you can put behind the %
    Since when?
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    Registered User raimo's Avatar
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    You should not use modulus operator before you know what it is.

    p / q = s + r/q

    p,q,r,s are integers. r < q

    Then also: p % q = r

    % 10 means that you take the last number of an integer.

    Therefore the values are not completely equally probable. This matters when you use a very large divisor.
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    Banned borko_b's Avatar
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    % is used for getting the remainder of a division...

    5 / 2 = 2 <-quotient
    5% 2 = 1 <- remainder 5 = 2*2 +1

    10/3 = 3
    10%3=1 -> 10 = 3*3 +1

    64/8=8
    64%8=0 -> 64= 8*8 + 0

  9. #9
    Seven years? civix's Avatar
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    SINCE DEV-C++ WAS CREATED, HAMMER!!!
    THOSE ARE THE GUIDELINES FOR DEV-C++

  10. #10
    Mayor of Awesometown Govtcheez's Avatar
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    Whoops...

    My original post wasn't totally accurate. The highest random value Dev-c++ 4 can produce is 32767, not a million, civix. Still, that's totally compiler dependant. It could be something totally different on Dev-c++ 5...

  11. #11
    Registered User raimo's Avatar
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    >the %10 means that the output will be between 0 and 10..

    THOSE ARE THE GUIDELINES FOR DEV-C++
    Your compiler can return 10 when taking mod 10? Would you tell me that for which x does this return 10: x%10 ? I don't think that Dev-C++ developers where so dummy that they created compiler which returns 10 when taking modulus 10. Same like if Microsoft created a compiler which returns 3 when calculating 3-2...
    I am not using Dev-C++.
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  12. #12
    End Of Line Hammer's Avatar
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    Originally posted by civix
    SINCE DEV-C++ WAS CREATED, HAMMER!!!
    THOSE ARE THE GUIDELINES FOR DEV-C++
    - no need to shout, I can hear you loud and clear.
    - You stated this
    one million is the highest number that you can put behind the %
    ... and I took that to be regarding the modulos operator (ie nothing to do with random number functions). Even if you were talking about the random() function, you're still wrong, as the number following % has nothing to do with the return from random().

    Eg if random() returned 32,000 and the calculation might be
    >32,000 % 1,000,001L
    which is perfectly valid, as far as I know, although the result will of course be 32000. Maybe you can put me right and prove it isn't valid?!
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  13. #13
    Mayor of Awesometown Govtcheez's Avatar
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    > Maybe you can put me right and prove it isn't valid?!

    No, you're right... it'll compile and run fine, but the value won't be over 32767 on Dev-c++ 4

  14. #14
    Just because ygfperson's Avatar
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    to get remainders in assembly code you divide a 64-bit number by a 32-bit number and get a 32-bit remainder and a 32-bit devisor. one million isn't even a power of 2. dev-c++ may have that limitation for some reason, but theoretically it should work fine with values in a normal integer's range.

  15. #15
    Seven years? civix's Avatar
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    ohhhhh ok....

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