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This is a discussion on Ask about random number within the C++ Programming forums, part of the General Programming Boards category; I want to generate random number between 1- 400,000 which is not the same value. Example. If X1 = 254899 ...

  1. #1
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    Ask about random number

    I want to generate random number between 1- 400,000 which is not the same value.

    Example.
    If X1 = 254899
    X2 not have the same value as X1.
    and X3 not have the same value as X1 and X2 .

    I want to generate data X1 - X400,000 which not have the same value and each data have value between 1-400,000

    If you know how to do that, please tell me. Thank you.

  2. #2
    End Of Line Hammer's Avatar
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    Random numbers, then just compare the new rand number with what you've already got. If its the same, get another random number.
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

  3. #3
    Seeking motivation... endo's Avatar
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    How long do you reckon that method would be good for Hammer? If you wanted a number between 0 and 100 but no duplicates, when does it take to long to reach the next number because you're throwing away duplicates?
    Couldn't think of anything interesting, cool or funny - sorry.

  4. #4
    End Of Line Hammer's Avatar
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    >How long do you reckon that method would be good for Hammer?
    Yeah, I suppose I didn't read the original question fully In answer to your question, not long, I suppose. My theory is good in the short term only. There must be a better way, but it's not coming to me at present...
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

  5. #5
    Seeking motivation... endo's Avatar
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    Wink

    Depends on the situation really. If you want 100 different numbers between 1 and 1000000, then it'll be fine. But if you want 80 random numbers between 1 and 100 a better method would need be to eliminate the 20 random numbers your not going to use. Maybe...
    Couldn't think of anything interesting, cool or funny - sorry.

  6. #6
    Cheesy Poofs! PJYelton's Avatar
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    I learned this with a program I wrote that shuffled cards.
    Code:
    int array[400000];
    for (int i=1; i<=400000; i++)
    {
      array[i]=i;  // first set each number equal to itself
    }
    
    for (int i=1; i<=400000; i++)
    {
       int x=rand()%400000+1;  // pick a random number between 1-400000
       // now switch this variable with the variable at the random number generated
       int temp=array[x];
       array[x]=array[i];
       array[i]=temp;
    }
    This will randomly place the numbers 1-400000 in to 400000 variables without duplicates

  7. #7
    Skunkmeister Stoned_Coder's Avatar
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    on computers its unfortuneate but some things have limits. One of those is the maximum number an int can hold.Also in the example shown RAND_MAX has surely been exceeded too. remember that rand() can only produce values up to RAND_MAX which on my system is 0x7fff
    Free the weed!! Class B to class C is not good enough!!
    And the FAQ is here :- http://faq.cprogramming.com/cgi-bin/smartfaq.cgi

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