Finding divisors

This is a discussion on Finding divisors within the C++ Programming forums, part of the General Programming Boards category; Ok the divisors of 10 are 1 , 2 , 5 , 10 . Ok I'm making a program, but ...

  1. #1
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    Angry Finding divisors

    Ok the divisors of 10 are 1 , 2 , 5 , 10 . Ok I'm making a program, but I can't think of a way to find the divisor of a number. Example if someone types 6 how do I find it's divisor? I just need help on te math portion.

    Note: I'm not asking people to do this code for me I just need some help on finding the divisor of a number.

  2. #2
    Chi! whiteflags's Avatar
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    Do you know how to build a factor tree?

    You can do this recursively. If it is even, divide in half, and factor again. If the number is odd, check for prime, otherwise factor the composite.

    1 and the integer are given factors of any integer.

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    Quote Originally Posted by citizen View Post
    Do you know how to build a factor tree?

    You can do this recursively. If it is even, divide in half, and factor again. If the number is odd, check for prime, otherwise factor the composite.

    1 and the integer are given factors of any integer.
    so num /= 2?

  4. #4
    Banned master5001's Avatar
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    You can do a very basic type of proceedure for brute forcing it.

    Example:
    Code:
    int nfactors(int number, std::vector<int> &factors)
    {
      int n = 0, i = 1, limit = number;
    
      factors.clear();
    
      for(;i < limit; ++i)
         if(!(number&#37;i))
         {
           limit = number/i;
           factors.push_back(limit);
           ++n;
    
           if(limit != i)
           {
              factors.push_back(i);
              ++n;
           }
         }
    
      // One could sort the results at this point, but bleh... you didn't specify that.
    
      return n;
    }

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    C++ Witch laserlight's Avatar
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    Quote Originally Posted by master5001
    You can do a very basic type of proceedure for brute forcing it.
    n seems rather redundant since there is factors.size().
    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

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    Banned master5001's Avatar
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    True.... I have no explanation for that other than I have been getting less and less sleep each passing day. Though, that is hardly a valid excuse for a programmer.

    Are you trying to reduce fractions, xbusterx? You could always use the Euclidean Algorithm. That would be a much more apt method for finding a greatest common factor.

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    Quote Originally Posted by citizen View Post
    Do you know how to build a factor tree?

    You can do this recursively. If it is even, divide in half, and factor again. If the number is odd, check for prime, otherwise factor the composite.

    1 and the integer are given factors of any integer.
    I know that but even numbers don't just divide by 2 , they divide by 3 , 5 , 5 etc as well. I know I have to use num % n1 = 0 . But ya I'm lost on the much part plz help.

  8. #8
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by xbusterx View Post
    I know that but even numbers don't just divide by 2 , they divide by 3 , 5 , 5 etc as well. I know I have to use num % n1 = 0 . But ya I'm lost on the much part plz help.
    So check all the numbers. num%2, num%3, num%4, ....

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    Quote Originally Posted by tabstop View Post
    So check all the numbers. num%2, num%3, num%4, ....
    ok what if I say this:

    Code:
    int n;
    cout << enter number;
    cin >> n; 
    
    for (int i = 1 ; i < n ; i++ )
    
    if ( n % i = 0 )
    how do I extract the divisor?

  10. #10
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by xbusterx View Post
    ok what if I say this:

    Code:
    int n;
    cout << enter number;
    cin >> n; 
    
    for (int i = 1 ; i < n ; i++ )
    
    if ( n % i = 0 )
    how do I extract the divisor?
    Divide?

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    Quote Originally Posted by tabstop View Post
    Divide?
    No that's not what I mean. IF ( n % i = 0 ) that means i is a divisor, but how do I extract the divisors so I can add them? sorry I'm new.

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    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by xbusterx View Post
    No that's not what I mean. IF ( n % i = 0 ) that means i is a divisor, but how do I extract the divisors so I can add them? sorry I'm new.
    You don't have to extract any divisors -- you just said that i was a divisor. So that's the number you have to add.

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    Quote Originally Posted by tabstop View Post
    You don't have to extract any divisors -- you just said that i was a divisor. So that's the number you have to add.
    exactly you're right , BUT how do I add them? that's why I need to exact the divisors to add them.

  14. #14
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by xbusterx View Post
    exactly you're right , BUT how do I add them? that's why I need to exact the divisors to add them.
    I usually add numbers with "+".

    I mean, you know what a running total is, right?

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    Quote Originally Posted by tabstop View Post
    I usually add numbers with "+".

    I mean, you know what a running total is, right?
    um like sum += num ?

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