Code:

#include <stdio.h>
#define maxsize 10
void quicksort (int a, int b);
//void mergesort ();
float ES26[11];
int i, j, k, x=1, mean, median, mode;
float *ptr, sum;
int main ()
{
printf("Input at most 10 floating point numbers, each entry followed by ENTER. \nInput 0 if you want to stop:\n");
for (i=1, j=1; j==1 || i==10; i++)
{
printf("%d) ", i);
scanf("%f", &ES26[i]);
ptr=&ES26[i];
if (*ptr==0)
{
x=i-1;
j=2;
}
if (i==10)
{
x=i;
j=2;
}
}
if (x==2 || x==4 || x==6 || x==8 || x==10)
{
printf("\nYou entered %i valid entries.", x);
ptr = &ES26[i];
quicksort(0, x-1);
printf("\nSupposed to Quicksort.");
}
if (x==1 || x==3 || x==5 || x==7 || x==9)
{
printf("\nYou entered %i valid entries.", x);
//meregesort
printf("\nSupposed to Mergesort.");
}
//ptr = &ES26[i];
for (i=1; i<=x; i++) //for printing
{
ptr=&ES26[i];
printf("\nEntry %i is %f", i, *ptr);
sum = sum + *ptr;
}
printf("\nThe mean is %f", sum/x);
getchar();
getchar();
getchar();
getchar();
}
void quicksort(int a, int b)
{
ptr=&ES26[a];
//*ptr=ES26[a];
int rtidx=0, ltidx=0, k=a, l=0;
float leftarr[maxsize], rtarr[maxsize];
//float pivot = ES26[a];
if (a==b) return;
while (k<b)
{
++k;
if(ptr[k] < ptr[a])
{
leftarr[ltidx] = ptr[k];
ltidx++;
}
else
{
rtarr[rtidx] = ptr[k];
rtidx++;
}
}
k=a; //reset k to a
*ptr=ES26[a];
for(l=0; l<ltidx; ++l)
ptr[k++] = leftarr[l];
ptr[k++] = *ptr;
for(l=0; l<rtidx; ++l)
ptr[k++] = rtarr[l];
if(ltidx>0)
quicksort(a, a+ltidx-1);
if(rtidx>0)
quicksort(b-rtidx+1, b);
}

here is an example of what I get if i run my program:

Input at most 10 floating point numbers, each entry followed by ENTER.

Input 0 if you want to stop:

1> 11.23

2> 43.553

3> 196.4673

4> 0.8874

5> 23.67

6> 90.5

7> 0

You entered 6 valid entries.

Supposed to Quicksort.

Entry 1 is 11.230000

Entry 2 is 11.230000

Entry 3 is 23.670000

Entry 4 is 11.230000

Entry 5 is 196.467300

Entry 6 is 90.500000

Can somebody help me point out where the mistake is? Thanks a lot!