Thread: computing median value

Hi,

I wrote a program that is using arrays that calculates sum, and avegare of the number user inputs (maximum 20 numbers). Now I'm trying to write one more function that sorts the array, and another function that computes median. I don't even know where to start with these functions. Please help me figure out the sorting function that sorts in ascending order.

As for the median function, I think that I could write a code that finds out whether the array has even or odd number of values and then if odd, just take the middle value; else, add two middle values and divide them by 2.

Here's my code so far,

Code:

#include<stdio.h>

/*Function prototypes*/
int getdata(double[],int size);
double computesum(int n, double x[]);
double computemean(int n, double sum);

int main(void)
{
        double x[20];
int size=0;
int n;
double sum;
/*Function calls */
        n=getdata(x, 20);
        computesum(n, x);
        computemean(n, sum);
}

/*This function gets data from the user */
int getdata(double x[],int size)
{
//int x[20];
//int size=0
int tmp;
int flag=0;
int n=0;
char cond, y;
   while(n<size && flag == 0)
    {
        printf("Enter a number\n");
        scanf("%d", &tmp);
        printf("Are you done? Press Y if yes, otherwise press N\n");
        scanf("%c", &y);
        scanf("%c", &cond);
        if (cond == 'n'){
            flag=0;
        }
        else if(cond =='y')
        }
        else if(cond =='y')
                flag=1;
        x[n]=tmp;
        n = n+1;
   }
        return(n);


}

double computesum(int n, double x[])
{
//int j;
//for (j=0; j<n; j++) printf("%f", x[j]);
int i;
double tmp;
tmp=0;
i=0;
int size;

while(i<n)
  {
        tmp += x[i];
        i = i+1;
  }

        printf("Sum of the values entered is %f\n",tmp);

        return(tmp);
}

double computemean(int n, double sum)
{

double mean, tmp;

mean=tmp/n;
        printf("Mean of the values entered is %f\n",mean);
}

Thanks

For sorting you could try implementing your function using something simple like the bubblesort algorithm.
For calculating the median, get ahold of the size of the array first then return the value of the middle element if the array size isn't divisable by 2 and return the mean of the two elements that share the place of being in the middle otherwise.

Here's my code with the sorting function implemented.

Code:

#include<stdio.h>

/*Function prototypes*/
int getdata(double[],int size);
double computesum(int n, double x[]);
double computemean(int n, double sum);
double computemedian(double x[], int n);

int main(void)
{

        double x[20];

int size=0;
int n;
double sum;

        n=getdata(x, 20);
        computesum(n, x);
        computemean(n, sum);
        double median = computemedian(x, n);

}

int getdata(double x[],int size)
{
//int x[20];
//int size=0
int tmp;
int flag=0;
int n=0;
char cond, y;

   while(n<size && flag == 0)
    {
        printf("Enter a number\n");
        scanf("%d", &tmp);
        printf("Are you done? Press Y if yes, otherwise press N\n");
        scanf("%c", &y);
        scanf("%c", &cond);
        if (cond == 'n'){
            flag=0;

        }
        else if(cond =='y')
                flag=1;
        x[n]=tmp;
        n = n+1;
   }
        return(n);


}

double computesum(int n, double x[])
{
//int j;
//for (j=0; j<n; j++) printf("%f", x[j]);
int i;
double tmp;
tmp=0;
i=0;
int size;

while(i<n)
  {
        tmp += x[i];
        i = i+1;
  }

        printf("Sum of the values entered is %f\n",tmp);

        return(tmp);
}
double computemean(int n, double sum)
{
double mean, tmp;
mean=tmp/n;
        printf("Mean of the values entered is %f\n",mean);
}

double computemedian(double x[], int n)
{
        int i;          /*Array elements*/
        int j;
        int k;
        int temp;       /*Temporary storage for some array element*/
        double median;
printf("before sorting, the array looks like:\n");
for (j=0; j<n; j++) printf("%lf\n", x[j]);
for (j = n; j>0; j = j-1)
        {
                k = 0;
                for (i=1; i<=j; i = i+1)
                        if (x[i]>x[k])
                                k = i;
                temp = x[k];
                x[k] = x[j];
                x[j] = temp;
        }

printf("after sorting, the array looks like:\n");
for (j=0; j<n+1; j++) printf("%lf\n", x[j]);

if (n%2 == 0)
{
        median = (x[(n/2)-1] + x[(n/2)+1]) / 2;
}
else
{
        median = x[n/2];
}
        printf("The median of all the input values is %lf\n", median);
}

The code compiles, but for some reason, after sorting my array is getting enlarged by one digit:

This is what i get before and after sorting.

Code:

Enter a number
7
Are you done? Press Y if yes, otherwise press N
n
Enter a number
3
Are you done? Press Y if yes, otherwise press N
n
Enter a number
7
Are you done? Press Y if yes, otherwise press N
y
Sum of the values entered is 17.000000
Mean of the values entered is 5.666667
before sorting, the array looks like:
7.000000
3.000000
7.000000
after sorting, the array looks like:
0.000000
3.000000
7.000000
7.000000
The median of all the input values is 3.000000

Any idea how i can preserve the size of the array?? That 0.00000 is not supposed to be there.

doesn't any one know how to fix this problem?