WA in GARDENAR

[rane]

Here is my code for the GARDENAR problem in SPOJ. I'm getting right answer in my system. Is this due to any precision issues?

#include<stdio.h>
#include<math.h>
int main ()
{
	int num,ipcount,a[10000],internal_count,i=0,index=0;
	scanf("%d",&num);
	ipcount= num;
	while(ipcount--)
	{   
	internal_count = 3;
	while(internal_count){
	scanf("%d",&a[i]);
	i++;
	internal_count--;
	}}
    while(num--)
{        
    double area,s;		
	s = (a[index]+a[index+1]+a[index+2])/2;   
	area=0.5*((((a[index]*a[index])*sqrt((double)3))/4) + (((a[index+1]*a[index+1])*sqrt((double)3))/4)  + (((a[index+2]*a[index+2])*sqrt((double)3))/4) + 3*(sqrt(s*(s-a[index])*(s-a[index+1])*(s-a[index+2]))));		
	printf("%.2f\n",area);
	index+=3;
}
return 0;
}