Help with function

This is a discussion on Help with function within the C++ Programming forums, part of the General Programming Boards category; In my first function "compute" if I want to return the values of "sum" and "sum_of_squares" in main what do ...

  1. #1
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    Arrow Help with function

    In my first function "compute" if I want to return the values of "sum" and "sum_of_squares" in main what do I have to do?
    Code:
    //Name: Joseph Valenzuela
    //Date: March 11, 2003
    //Purpose: To design and implement my own program for project1.
    
    #include <iostream.h> // For output to the screen and input from user
    #include <fstream.h> // To allow input and output streams
    #include <stdlib.h> // Contains exit function
    #include <math.h> // Contains square root function
    
    double compute();
    //Precondition:
    //Postcondition:
    double mean(double xnum, double sum);
    //Precondition:
    //Postcondition:
    double deviation(double var);
    //Precondition:
    //Postcondition:
    double variance(double sum_of_squares, double xnum, double avg);
    //Precondition:
    //Postcondition:
    
    void main()
    {
      
    double xnum,sum,avg;
    ifstream input_data;
    
    
    cout <<"\nWELCOME TO THE BASIC STATISTICS PACKAGE!\n";
    
    cout << "Enter amount of numbers to be evaluated: ";
    cin >> xnum;
    
    
    
     sum = compute();
     avg = mean(xnum, sum);
    
     cout << sum << endl;
     cout << avg << endl;
    
    }
    
    double compute()
    {
    
      double sum=0, sum_of_squares=0, in_num=0, count=0;
      ifstream input_data;
    
     input_data.open("stats.dat");
     if (input_data.fail())
       {
         cout <<"Input file could not be opened.\n";
         exit(1);
       }
    
      input_data >> in_num;
      while (!input_data.eof())
        {
          count++;
         sum += in_num;
         sum_of_squares += in_num*in_num;
         input_data >> in_num;
        }
      
      return(sum);
      return (sum_of_squares);
      
    }
    
    double mean(double xnum, double sum)
    {
      double avg=0;
    
      avg = sum/xnum;
      return(avg);
    
    }
    
    double variance(double sum_of_squares, double xnum, double avg)
    {
      
      double var=0;
      
      var = (sum_of_squares/xnum) - (avg*avg);
      return(var);
      
    }
    
    double deviation(double var)
    {
    
      double dev;
      
      dev =  sqrt(var);
      return(dev);
    
    }

  2. #2
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    Lightbulb one more question

    If I wanted to compute the median of all the numbers in my input file, in this program what would be the best way to go about this? Thanks!

  3. #3
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    Re: Help with function

    Originally posted by 3kgt
    In my first function "compute" if I want to return the values of "sum" and "sum_of_squares" in main what do I have to do?
    Code:
    //Name: Joseph Valenzuela
    //Date: March 11, 2003
    //Purpose: To design and implement my own program for project1.
    
    #include <iostream.h> // For output to the screen and input from user
    #include <fstream.h> // To allow input and output streams
    #include <stdlib.h> // Contains exit function
    #include <math.h> // Contains square root function
    
    double compute();
    //Precondition:
    //Postcondition:
    double mean(double xnum, double sum);
    //Precondition:
    //Postcondition:
    double deviation(double var);
    //Precondition:
    //Postcondition:
    double variance(double sum_of_squares, double xnum, double avg);
    //Precondition:
    //Postcondition:
    
    void main()
    {
      
    double xnum,sum,avg;
    ifstream input_data;
    
    
    cout <<"\nWELCOME TO THE BASIC STATISTICS PACKAGE!\n";
    
    cout << "Enter amount of numbers to be evaluated: ";
    cin >> xnum;
    
    
    
     sum = compute();
     avg = mean(xnum, sum);
    
     cout << sum << endl;
     cout << avg << endl;
    
    }
    
    double compute()
    {
    
      double sum=0, sum_of_squares=0, in_num=0, count=0;
      ifstream input_data;
    
     input_data.open("stats.dat");
     if (input_data.fail())
       {
         cout <<"Input file could not be opened.\n";
         exit(1);
       }
    
      input_data >> in_num;
      while (!input_data.eof())
        {
          count++;
         sum += in_num;
         sum_of_squares += in_num*in_num;
         input_data >> in_num;
        }
      
      return(sum);
      return (sum_of_squares);
      
    }
    
    double mean(double xnum, double sum)
    {
      double avg=0;
    
      avg = sum/xnum;
      return(avg);
    
    }
    
    double variance(double sum_of_squares, double xnum, double avg)
    {
      
      double var=0;
      
      var = (sum_of_squares/xnum) - (avg*avg);
      return(var);
      
    }
    
    double deviation(double var)
    {
    
      double dev;
      
      dev =  sqrt(var);
      return(dev);
    
    }
    void main(), what the hell? main() returns an int.
    You can only return one value from a function. However, you could pass two parameters to your compute function (one for sum and one for sum of squares) and use them as return values. For example:
    Code:
    void compute(double& sum, double& sum_of_squares)
    {
      sum = sum_of_squares = 0;
      double in_num=0, count=0;
      ifstream input_data;
    
     input_data.open("stats.dat");
     if (input_data.fail())
       {
         cout <<"Input file could not be opened.\n";
         exit(1);
       }
    
      input_data >> in_num;
      while (!input_data.eof())
        {
          count++;
         sum += in_num;
         sum_of_squares += in_num*in_num;
         input_data >> in_num;
        }
    }
    Then call it like this:
    Code:
    double sum, sum_of_squares;
    compute(sum, sum_of_squares);
    After that function call, sum and sum_of_squares will hold the values given to them in the function.

  4. #4
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    Re: one more question

    Originally posted by 3kgt
    If I wanted to compute the median of all the numbers in my input file, in this program what would be the best way to go about this? Thanks!
    This is how *I* would do it:
    Code:
    #include <vector>
    #include <algorithm>
    
    // ... 
    
    double median()
    {
       std::ifstream fin("log.txt");
       std::vector<int> medianvec;
       double val;
       while (log >> val)
           medianvec.push_back(val);
    
       std::sort(medianvec.begin(), medianvec.end());
       int size = medianvec.size();
       if (size & 1)
          return medianvec[size/2];
       else  // What are you supposed to do with two medians? Get the average?
          return (medianvec[size/2] + medianvec[size/2-1]) / 2;
    }
    Basically, read all integers into an array, sort the array and return the element at array size / 2 (middle of the array).
    Last edited by Eibro; 03-12-2003 at 12:34 AM.

  5. #5
    nag
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    Re: Re: Help with function

    Originally posted by Eibro
    void main(), what the hell? main() returns an int.
    Why are you are worrying about it so much,
    I have a book
    Microsoft's Guide To C++ Programming.
    In this book the writer throughout used void main() in all code examples (yes the creators of VC++)
    Two men looked out from Prison Bars,One saw the mud,the other saw stars.

  6. #6
    Veni Vidi Vice
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    Why are you are worrying about it so much
    ....
    ...
    ...
    ...
    Spare us the time and make a search on this board on the topic. It has been covered gizillions time!!!

  7. #7
    nag
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    yes but most newbies dont see faq nor anybody tells them about this!
    Two men looked out from Prison Bars,One saw the mud,the other saw stars.

  8. #8
    Veni Vidi Vice
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    yes but most newbies dont see faq nor anybody tells them about this!
    Hmmm I find it very hard to miss them. Well, there is a FAQ board and a faq button(upper right). Maybe we should ask the mod the make then larger (no sarcasm)... well I donīt now. How(where) would you like them to be????

  9. #9
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    or you could download a more standard compliant compiler, newer compilers; and try to compile void main. you will get errors. it is not standard. if you want to know what, go to Bjarne Stroustrup's site; check the FAQ, as well.

    Just click here. It is a link to the faq.

  10. #10
    Mayor of Awesometown Govtcheez's Avatar
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    > faq button(upper right).

    That's the FAQ for using vBulletin. The rules and stuff are in the Programming FAQ link at the bottom of the page.

    > yes the creators of VC++

    So they wrote a compiler. Who cares? They didn't invent the language.

  11. #11
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    Arrow Thanks eibro

    Hey thanks for trying to help me out with that, I am trying the call by refrence right now, I dont think I can compute the median that way because we haveent learned the algorithm or vector libraries. I think for the median I have to close my input file then reopen it to catch the middle numbers and if it is even I have to average the two middle numbers and if it is odd I can catch the middle number and return that value. What do you think?

  12. #12
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    sounds like a good learning exercise to me. If you store your input in an array and keep track of the indexes used you can use the index to help you determine the median. Say the last index used was 2. That means there were 3 items read in and the median is at index 1. If the last index was 99 then there were 100 items read in and the median is the average between the value at index 49 and index 50. Since you already know what xnum is going to be, user has to input the value!, then the last index is xnum - 1 and you can go from there.

  13. #13
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    Arrow My median function

    Ok guys here is what I came up with for my median function, but I am still getting a compiler error saying that it expects a statement before the else? How should I fix that?

    Code:
    double median (int xnum)
    {
      double median,med_pos,count=0, temp;
      ifstream input_data;
      
      
        input_data.open("stats.dat");
        if (input_data.fail())
          {
    	cout <<"Input file could not be opened.\n";
    	exit(1);
    	
    	med_pos = xnum/2;
          }
        
    if ((xnum%2)==0)
          {
    	median=0;
    	while (input_data >> temp)
    	  {	
    	    count++;
    	    if((count==med_pos)||(count==med_pos+1))
    	     	median = median + temp;
    	  }
        
        median = median/2;
         
          }
        return(median);
        
        
        else if ((xnum%2)!=0) 
          {
    	median=0;
    	while (input_data >> temp)
    	  {	
    	    count++;
    	    if(count==med_pos+1)
    	      median = median + temp;
    	  }
    	median = median/2;
          }
      
      return(median);
      
      }

  14. #14
    C++ Developer XSquared's Avatar
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    Remove the return statement before the else statement.

    Code:
    	...
    	median = median/2;
    }
    //return(median);
    else if ((xnum%2)!=0) 
    {
    	median=0;
    	...
    Last edited by XSquared; 03-12-2003 at 07:33 PM.
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  15. #15
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    Arrow Thanks, but is there anything wrong with the code?

    Hey thanks that fixed it and now it compiles correctly but how come it doesnt return anything, it returns 0 every time, is there something wrong with the code?

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