Standard deviation

This is a discussion on Standard deviation within the C++ Programming forums, part of the General Programming Boards category; Code: //Here is what I got so far #include <iostream> using namespace std; int main () { int n, median; ...

  1. #1
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    Standard deviation

    Code:
    //Here is what I got so far
    #include <iostream>
    using namespace std;
    
    int main ()
    {
      int n, median;
      double standarddeviation;
      int num [31]={12, 13, 15, 16, 18, 19, 21, 34, 57, 32, 38, 213, 10, 14, 156, 172, 134, 143, 132, 139, 751, 30, 31, 81, 23, 41, 24, 51, 75, 91, 1234};
      int sum= 0;
      for (n=0; n<31; n++)
      sum = sum+num [n];
      double average=sum/31.0;
      standarddeviation=(num[n]-average)*(num[n]-average);//I want to multiply every number by itself, subtract from the mean and son on but I can't seem to get it
      cout<< sum<<endl;
      cout<<average<<endl;
      cout<<standarddeviation;
      return 0;
      
    }

  2. #2
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    does this make your problem clearer?

    Code:
      for (n=0; n<31; n++)
      {
      sum = sum+num [n];
      } 
      double average=sum/31.0;
      standarddeviation=(num[n]-average)*(num[n]-average);//I want to multiply every number by itself, subtract from the mean and son on but I can't seem to get it

  3. #3
    Algorithm Dissector iMalc's Avatar
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    Look at the standard deviation formula again. In no way does it involve an average as part of the calculation.
    You also need to calculate the sum of the squares of the input data as well as just the sum of the input data.
    Last of all, you will need the square root function.
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  4. #4
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by iMalc
    Look at the standard deviation formula again. In no way does it involve an average as part of the calculation.
    But it does, specifically, the mean.
    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. #5
    Algorithm Dissector iMalc's Avatar
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    Quote Originally Posted by laserlight View Post
    But it does, specifically, the mean.
    Well it's squared, that's what I meant.
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