Thread: Random Function

  1. 01-06-2009 #1
    T1m
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    Random Function

    I have a question regarding the random function.

    In the program I'm building I have a function where a random number is needed

    Code:
    randomnumber = rand() %3 + 1
    but I also have to repeat the function 3 times

    but when I repeat the function 3 times, the random number in all 3 cases is exact the same

    does anyone know how I can avoid this?

    ps: I'm using codeblocks and I included time.h for this function
  2. 01-06-2009 #2
    matsp
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    You may need to post your code - I would guess that you are calling srand() multiple times with the same (or very similar) value.

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  3. 01-06-2009 #3
    kermit
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    Besides what Mats said, have a look at this and this.
  4. 01-06-2009 #4
    laserlight
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    There is also the possibility that you are not using srand() at all, and it so happens that the first three numbers generated are the same modulo 3.
    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
  5. 01-06-2009 #5
    T1m
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    my problem seems to be solved, I initialised the srand() in a loop, and that seemed to be the problem
  6. 01-06-2009 #6
    matsp
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    Quote Originally Posted by T1m View Post
    my problem seems to be solved, I initialised the srand() in a loop, and that seemed to be the problem
    Yes, that is definitely a bad thing to do - it is almost always wrong to call srand() more than once in a program - the only time it actually makes sense is when you actually WANT to repeat the same sequence of random numbers for some reason.

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    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.
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