Thread: Student Having Problem With Reference Parameters

Alright, so... I've got a program that needs to find the mean and standard deviation of a number of scores that are inputted by the user.

Of course, for this assignment, I need to use arrays and reference parameters... I also need to use a bubble sorting method to sort the scores into decending order.

I have the bubble sorting and the arrays taken care of-- I'm just having problems with the reference parameters.

In a number of unncessesary functions, I have this:

Code:

#include <stdio.h>
#include <math.h>

void inputData(int list[], int* n),
bubbleSort(int list[], int n),
statistics(int list[], int n, double* mean, double* stdv),
display(int scores[], char grades[], int n, double mean, double stdv); 
char letterGrade(int score, double mean, double stdv);


#define max_class_size 40

int main()
{
    int list[max_class_size], classSize, exit, i;
    double mean, stdv; 
    
    printf("How many scores?> ");
    scanf("%d", &classSize);
    
    printf("Enter scores>");
    inputData(list, &classSize);
    bubbleSort(list, classSize);
    statistics(list, classSize, &mean, &stdv);
       
      
  
    for(i=0 ; i < classSize ; i++)
    {
            printf("%d\n", list[i]);
     }
     
     
     
     printf("Exit program? (y/n)> ");
     scanf("%d", &exit);
     



        
}


void inputData(int list[], int *n)
{
     int i;
     
     for(i=0 ; i < *n ; i++)
         scanf("%d", &list[i]);

          
 }
 
void bubbleSort(int list[], int n)
{
     int a, b, i;
     
     for(i=0 ; i < n-1 ; i++)
         {
             for(a = 0 ; a < n-i-1 ; a++)
             {
                   if(list[a] < list[a+1])
                   {
                              b = list[a];
                              list[a] = list[a+1];
                              list[a+1] = b;
                   }
                   
             }
         }

 }

void statistics(int list[], int n, double* mean, double* stdv)
{
     int sum, sum_sqr, i;
     
     for(i=0 ; i < n ; i++)
     {
             sum += list[i];
             sum_sqr += list[i] * list[i];
     }
             
     *mean = sum / n;
     *stdv = sqrt(sum_sqr / n - *mean * *mean);
     
}


char letterGrade(int score, double mean, double stdv)
{
     
     

 }
 
void display(int scores[], char grades[], int n, double mean, double stdv)
{  
}

I know, the last two funtions at the end, I haven't filled in. Those are to be eventually filled in.

I'm having no problem with the *n reference parameter in the inputData function. That's working just fine. However, in the statistics function, I'm not getting what I want when I try to print mean and stdv.

When I try to print mean and stdv, this is what I input, before the for loop to print the scores in decending order, but after I call on the statistics function:

Code:

    printf("\n\nmean: %.2f\nstdv: %.2f\n\n", mean, stdv);

When i use the & symbol infront of mean and stdv in the printf, I get values of 0 for whatever I input.

However, if I input 3 numbers, say; 98 88 77
I get this output:

mean: 66974062.00
stdv: -1.#J

...And that certainly isn't correct.


What did I do wrong?



Thanks!

Okay, I just figured out why I was getting such ridiuclous values for the mean and standard deviation.

I needed to set sum and sum_sqr to 0, initially. That fixed everything. ...Now on to new problems.